Am I pregnant? Missed period and strange symptoms.

Hi, I had unprotected sex around the time my period was due (it normally comes at around the same time every month give or take a week), but that was over three weeks ago so I've completely missed it. I've had fairly heavy discharge, have been feeling very tired and have had really uncomfortable lower back pain. I've also been feeling nauseous, especially when I haven't eaten in a while. I've taken multiple tests and all have come back negative, but something still just doesn't seem right. Do I need to leave it a little longer to test? Thank you xxx