I'm 21 years old and I haven't had my period for 6 months. In September I took a pregnancy test and it was negative. Since then I haven't been feeling to well. I've been having sharp chest pains, stomach pains, headaches, dizziness sometimes, not sleeping well, and gaining weight. I have a irregular period, but this is the longest I haven't got it. I need to know why and what can it possible be?