thyroxine tablets give me sore stomach

im 14 and got diasgnosed with a under active thyroid when i was 11 years old the symtoms started to occor when i was about 8 and my mum took me took the doctors and they said she needs to take for long walks and buy less sweets i was crying cos i took my dog walks everyday went to dancing/drama twice a week and went on my trampoline every day and when i went friends houses their mums talk to my mum and they didnt understand how i was fat when i ate normaly and i also fell asleep alot and people at school who didnt understand bullied me and when i was 10 my mum took me back to the doctors and they said i should get my tonsils remive which didnt help at all and when i was 11 my mym went to other doctor and begged for a blood test and i was then diagnosed with an under active thyroid i was put on thyroxine tablets and lost wait extremely fast and by the time i was in first year at high school i was back to normal weight but then a picture of my class in primary 7 was posted on facebook and there was 500 coments about me reported them but at school people said i must of got liposuction which i f*****g didnt and my eyes were stiill puffy which i got called fish but now ive moved school and im happier but im getting stomach stabbingpains in my lower stomach after taking thyroxine im on 125 and my doctor said its the dose so i thought the pain could be to do with my periods but i get every morning straight after taking the tablets as well as added stomach and back cramps and feeling like im going to be sick when on period its also really heavy and i cant go on birthcontrol cos it reacts with my thyroxine tablets plz help im in pain and not at school just now :(