Has anyone gone through this??

This is kind of a story but please help me out? so this is the situation I’m currently going through and first I’m going to say I’m 19 and yes I’m currently sexually active. I was supposed to get my period on this Friday but when me and my boyfriend had sex yesterday It started I was bleeding so I put a pad on and I was even feeling my regular period symptoms which are lower back pain,cramps, and sore breast but the cramps would only come like every so often, they weren’t and still aren’t frequent and that’s what I’m used to. So after I put the pad on a few hours later he took me home and I went to the bathroom and there was literally the smallest spot of blood and when I wiped my self there was nothing on the toilet paper it was literally clean I’m still so confused because after me and my boyfriend had sex there was a lot of blood and now I’m literally just spotting. So after that I took a shower and went to just go chat with him on the phone before I went to bed and I started feeling extremely nauseous and it freaked me out so I took a pregnancy test but it was negative now I don’t know what to do because the nausea won’t go away and my period blood is so little and is looking kind of brownish and looks like it’s mixed with white discharge but it looks mainly like discharge.