Not sure..

Im Katie. I'm 17 years old, and I had sex July 31st. I've been experiencing a lot of abdominal pain and my tummy has gotten gotten hard and bigger. I've taken at home pregnancy tests and they come out negative. And ive been getting my period. but I have almost all of the symptoms.. I think I have all of the symptoms but vomitting, and my breasts are kind of sore and tender. but not as bad as I thought?

please help!