What Causes Weight Gain And No Periods For 4 Months?

i havent had my period in about 4 months and before that i was on some medicine my gynocologist gave me she said it would give me my period after the 10 day period well it did for 10 days very heavy after that nothing i have been breaking out constantly and have a little fuzz on my face and my skin is extremely oily im constantly gaining weight and losing my gyno sent me to get a sonogram and she said nothing showed up also had blood test done and my general doctor told me my hormones are fine.