pms extreme symptoms

I'm turning twenty tomorrow. I've never suffered from horrible period symptoms. I get the occasional cramps and back ache but for the past two months I've gotten nausea, migranes, breast tenderness, I'm hungry all the time, I'm super emotional, crying over everything, I get dizzy and oh god the chocolate. love it. But I get these symptoms for 20 days out of my 25 day cycle! I got tested to make sure I wasn't pregnant but the migranes and hunger has been effecting my job! before the last two months I never had these symptoms as extreme or as long as they have been. I experience them normally for maybe three days before my period. My period was always regular before this and my diet had not changed. What's going on? Has this happened to anyone else?