What Causes Delayed Periods With Abdomen Cramps?

hi, i havent gotten my period in about two months. i am sexually active but i did take two hpt and they both came back negative. i dont know whats going on. i have random cramps but no period. i also have noticed im tired more often and have been really hungry lately. ive been peeing alot more but i think thats because ive been drinkning more... but no fark areolas around my nipple.
thanks