Hello,
I am 19 and have always had painful (extreme) periods, but over the last year my monhtly has evolved. I went from major pain once a month to bearable (with major motrin) pain twice a month. The whole weight gain is terrible as it is all in my tummy and thighs (I NEVER gain weight in these areas). I am 5'11 and went from 118 to 128 (136 on my period). I have had a cyst rupture in the past and now am not sure what to do now.

See your doctor to get some tests done.
A friend of mine had poly cystic ovary syndrome which caused very irregular periods and huge weight gain.