Well im not sure. Honestly but I read what you wrote and I heard you could still have your periods if you are pregnant so you dont want to rule that out yet.
Honestly you should Probably go to the doctor. to get it checked out for sure.
wait a little and see how your symptoms are. but even still your gonna have to get a test probably to know for sure all girls bodys are different. and dont always act the same. If your not wanting to get pregnant I wouldnt let guys sperm in me everytime you are sexually active. Im sure you are aware of this. But having sex partners like your having them One guy today and the next guy tomorrow is really un healthy hun. your gonna have to take care of your self there are alot of things you can catch. well good luck (: hope my advice helped some.