Loss of Appetite

My 1st instinct is the meds and the infection are making him not feel well but his weight being that low is concerning. I would push the Dr. and/or get a 2nd opinion. Try to get your son to drink some toddler formula (the ones formulated for older ages - not "baby" formula - I'm pretty sure Carnation has one). Also, perhaps some whole milk. You need to make sure he doesn't have anything else going on from that bug bite i.e. Lyme Disease, etc. Not to scare you but it's worth researching just to be sure. Hopefully it's just the meds and he'll bounce back soon!

A decrease in appetite is normal for this age, especially if he might be on meds that could affect it, but does he really not eat ANYTHING on some days? That would be a concern to me. Even if he's only eating a little bit like some fruit, protein, drinking milk, whatever. It seems like toddlers can't survive on what they eat in a day, but truly they can and usually the next day they eat a little bit more. During the course of the week they've usually eaten what they "should" eat or at least close to it. But, if he really isn't eating anything I'd probably call the doctor back.

As long as he is still active and has rosy cheeks, I wouldn't worry. Kids go through periods of time where they will hardly eat anything, followed by a few weeks where they want to eat constantly. As long as they look healthy and they are energetic, I have stopped even thinking about it. Also, pediasure will make him feel full, so I would hold off on giving him any of that unless your doctor recommends it. The nutrition from real food is better for him than a Pediasure drink. Keep in mind also that as kids grow, they will lose weight (using their energy to gain height rather than gain weight). Losing a pound at 1 year old is probably not that big a deal in the grand scheme of things - both of my girls did that as they grew taller! Also, my younger daughter has been in the 15% since she was a year old - she was born big, and then settled into a growth pattern along the 15% line. Someone has to be smaller than average in life, and it's okay! Try not to worry! (I know that is easier said than done for us mommies!) ;)

Being on an antibiotic not only kills bad bacteria, but the good bacteria that lives in your stomach. Your son may just not be feeling hungry or could get nauseas when he eats. Try giving him some yogurt that works with my daughter who has a very sensitive digestive system. All my babies fell into the 25% at their 12 month check-up. My doctor's explanation for it was that they usually have a growth spurt around that age and were also getting ready to walk or starting to walk so were burning extra calories. If you're really worried take him in about 6 weeks from his last appointment and ask for a weight check.

I would call the Dr back and push the issue. If the Dr is not concerned and you are, you should find out why the lack of eating is not a big concern. The Dr should be able to put your mind at ease. OR, by pushing your case, make the Dr realize exactly what is going on. Perhaps s/he does not fully understand the situation.
At the very least, the Dr should recommend something to keep up nutritional intact. My first thought is to try to feed your little one some formula since it is full of nutrients for a toddler and may be more filling than nursing, especially if you are only counting on nursing as a snack at this stage.
I am sure the lack of appetite is due to your little guy not feeling well and as soon as this infection is gone his appetite will return with a vengence. My 12 month old had a greatly reduced appetite for about a week after her vaccines which gave her a mild fever. She did drink her formula though so I did not worry too much about the amount of solids she was taking, as she did eat a bit each meal.
Hang in there!

bactrim is typically used for infected tick bites, not regular bug bites, the disinterest in eating may be a side effect of the medication. try using non scented soap and shampoo for the child., bugs lose interest in a child that doesnt smell like flowers, flowers are food to bugs after all
any doctor worth going to, should be concerned when a child stops eating, for any reason. find another doctor
K. h.

My son is also in the low weight percentile, he even dropped between his last two doc visits! She wouldn't even tell me the percentile, but it's below the 25th where he's always been. :\

He always has been a low weight percentile, since BIRTH. But it makes me nuts. I know I am not very rational when it comes to my son's weight and worrying about it. ;) Is he a super active little guy? Sometimes when I watch my son prancing from here to there ALL day long, I can't believe I'm shocked by his skinny tendencies! :)

Yes, being sick and the antibiotics can make him lose his appetite. If your doc isn't worried, then you should do your best not to worry. My son is 28 mo and I have slowly learned that he has appetite "cycles". He'll eat well for a few weeks and then not so much for a few weeks. When he's in a low cycle, yes, I feel like he'll wither away and die and when he's eating well, I'm delighted beyond belief!

Def don't overreact. I can tell you from first hand experience that while your son may cooperate now, as he gets older and exerts more of his independence when you push him to eat he will pull away and refuse even more. :) We have just been working on this for the last 3 weeks. I was trying to get him to eat ALL the time and he was finally refusing to come to mealtime at all. Now that I act like I don't care (I SOOO care) and even limit his snacking (kills me to limit his food!) he is properly hungry and is happy to eat!

This video REALLY helped me to chillax, I have literally watched it about 10x. It really comforts me when he's in a low eating cycle:
http://www.youtube.com/watch?v=eQ3sC_4ga1M

Good luck mama! You're doing a great job and some kids are just thin and active. Think about your son's intake over a whole week even a month--not meal to meal. Kids eat when they're hungry! They won't starve. Even we skip meals sometimes. :)