My hypothyroidism was identified right before my
pregnancy - and it got REALLY bad during that
pregnancy. In my case, it was difficult to diagnose because I had a normal TSH, but a low Free T4. Finally, in the past two years, I have begun to lose weight - I am down to 175 from 225, but it HAS been a struggle. However, I did not GAIN more weight after starting on Synthroid (except during my pregnancy, of course).