What Causes Irregular Periods, Weight Gain, And Fatigue?

I have been experiencing weight gain, fatigue, bloating, flatulence, head aches, deteriorating hair, irregular periods, difficulty conceiving, memory issues, fogginess in my brain, irritability and anxiety. I'm only 23...I just got my thyroid tested and apparently its "within normal range". I'm 5' 6" and weigh 138 (the most I've ever weighed in my life).