I was diagnosed with hypothyroidism when I was 12 (15 years ago) and have been on Synthroid ever since. The last year or so I've been taking the generic brand and I think it's worked better
for me than the name brand. I can't remember the dosage I'm on, I think it's fairly high. I can always tell when I'm too low, not because I'm necessarily over tired but because my brain literally stops working, I can't speak in complete sentances, I get
really forgetful, I'll be driving and forget how I got where I am, etc.
It's been so long since I started taking meds that I can't remember how long it took me to "feel better", I had such bad emotional problems from the whole ordeal though that I probably didn't really notice anyway. I know now when I'm on too low a dosage it takes a couple weeks for me to feel "normal" again.
Also, since you just started taking it, it might be awhile before you feel "normal" or "better" because the DR should start you out at a very low dosage and work you up because it can damage your heart - unless you should be taking a very low dosage. When I first started on it I had chest pains (freaky to have chest pains at 12 years old!) and still do every now and then if my dosage gets changed. My mom is also hypothyroid, she got diagnosed a few years ago and the DR would only start her out w/ a low dosage and work up slowly so it wouldn't damage her heart, it was probably a year or so before she started to feel better, but she had to work up alot.
Don't get discouraged though, it does get better!
You just have to learn what your body can handle and not to overdo it, and it's also very important that you family also understands this. And
never, never, never, never stop taking your meds unless the DR says so!!!!