I had unprotected sex two weeks ago and now I'm having lower back pain and lower stomach pains dizzy, gagging, going to the bathroom a lot more, having bad cramps, when I lay on my stomach it hurts but when I lay on my side it stops and I took a home pregnancy yesterday and it said I wasn't

Assuming you took the test at the right time (when you've missed your period), it's almost certain that you are not pregnant. Things like cramps, peeing etc tend to happen around the time your period is due, and worrying about pregnancy can account for the rest.

Well ii had sex on 13th of April and I took the test yesterday. I'm always tired and back really hurts and my stomach feels full on the inside

Have you missed your period yet? Did you take the test using first morning urine?