Why Am I Missing Periods?

I have missed my period for 4 months then took birth control and had it then i stopped taking it and missed my period again now for 1 and a half months.,if u should know I haven't had sex in 3years. I wake up every morning SUPER nauseas and I'm ALWAYS tierd..like I've been up for days. My right foot hurts all the time unless I've been on it for a while. When it first started the back of my head felt like it was hit with a baseball bat for 3 days. What in the world is wrong with me?