What Causes Side And Back Pain With Cramps And Delayed Periods?

since the begging of this month ive been feeling really sick, at first i was really stressed to the point i thought i was making myself sick, ive had lower and upper back pain as well as what felt to me like menstral cramps but it was still too early for my period ,which i must add still hasnt come yet. for the first 2 1/2 weeks everything i ate made me gagg even the smell of food made me sick. i fall asleep earlier than usual as well. i did take a pregnancy test because i was unsure but that turned out negative. as of a few days ago the pain wasn't as bad , then last night i had bad cramps which i thought was my period coming but it wasn't. what could possibly be wrong with me ? i still feel back , and side pain as well as menstral cramps. help!