I was bleeding two days after unprotected intercourse, I am really tired and I have back pain

I'm on the birth control patch. I had sex 2 times unprotected. I bled for 2 days while I was wearing the patch then stopped and spotted for one. When it was time for my real period to happen the week after it didnt come. I have been really tired, having lower back pains and cramping feelings in my lower stomach and headaches and some nausea without vommiting and lack of appetite. Took a home pregnancy test and got a light blue line saying positive but went to the doctor and had a negative pee test. But i still feel funny and not like myself. Help!