Why Am I Having No Menses From Past Few Years?

hi doctor.. since 1 was 14 years old i age attended.. now am 21 my periods s not in proper manner..after age atteneding i was not get my period for 2 years then i took medicines .. so tat i get my periods cycle as 3 months once or 2 months once. and for past 4 years my periods s not coming..i became little bit fat now.. wat to do.. give me any suggestion