my thyroid pills dont work anymore? wrongly diagnosed?

im still always tired. ive been on synthroid for a year and a half now. just had my levels checked in october and there fine she says. what else could cause ur ths or ts to be very low? and make u tired? im on 100mcg. could it just be my thyroid dropped that low in the last few months? im sick of being tired.
the synthroid stopped my migrains, ive only had 4 in the last year. i found that strange too. but she said it was normal to help stop them too. i think im going to get another doctor.
the last few weeks my head feels like theres pressure in there or something i cant really explain the feeling. its weird and scary.
i just go to a reg family doctor