I was showing after a month with my first pregnancy and it made me wonder if I was having more than one since all my girlfriends didn't start showing until three months into their pregnancies. I had my first OB appt. at 3 1/2 months and the doctor didn't think I was having more than one.
A different doctor in the same practice saw me at 4 1/2 months; he said the same thing. I kept wondering, though, if I was carrying more than one. I couldn't shake eth belief that I was.
At my third check-up at 5 1/2 months, I had yet still a third doctor examine me. She said that I was either having more than one or that my due date was wrong! So she gave me my first ultrasound and discovered taht, sure enough, I was pregnant with two!
So, the lesson here is, go get an ultrasound so that you can either find out you are carrying more than one or to rule it out!