My parents think I'm pregnant

Hi. I am 17 years old and I have been with my boyfriend for one year and a half. We have been having sex all this time but my parents don't know because they don't agree with that. Yesterday i began feeling nauseas and diarrhea and they are convinced I am pregnant. I am really scared but I had my period last week and we haven't been together since that. What should I do? What donyou think I have? Ibam pretty worried and they want to take me to the hospital with them.