What Causes Abdomen Pain, Tender Nipples And Loss Of Appetite?

my periods have been really irregular and short for the past couple of months (they have never been irregular) latley i have been nauseas and having a loss of appetite and mild lower adominal pains. And i recently noticed my nipples have been extremely tender about 4 days before my period which was never a pms symptom. i have taken several pregnancy tests and they are all negative so what can this be? im a 22 year old female