I have had hypothyroidism since I was 13 (I am now 42). To me, it's really not a big deal. I am always careful to do just a few things:
1: I take my Synthroid every day at the same time every day.
2: I "listen" to my body. If I begin to feel tired, have weight changes or moodiness, I talk to my doctor. I went through a period of time that one of my doctors wanted to put me on hormones, but it turned out my thyroid dosage just needed to be changed.
3: Have your thyroid level checked often, especially right at first. If you look in the mirror and it looks like you have a big "adams apple", give the dr. a call and have your labwork done.
4: Always insist on the brand name Synthroid. Don't get the generic. I have been told by several doctors that with this particular drug, it is hard to get the exact dosage with the generic. This is one case that the trade name (Synthroid) is actually very inexpensive.
Like the other post mentioned, there are a lot worse conditions out there. This is an easy one. Yes, you will take Synthroid for the rest of you life, but big deal. I count my blessings that I'm not diabetic, I don't have cancer, or any other big, bad illness.
Good luck to you and keep us posted.