Implantation bleeding after period?

Okay I know this sounds crazy. But I’m a little confused. So my boyfriend and I had sex on my period for the first and second day. Yes some got in on the second day. I didn’t think anything of it and I have a seven day period every time. But the next day my period did a complete turn around. I was no longer bleeding for that whole day (day three). Day four I didn’t even have a period I would wipe and it was only smears of light pink. My period came to a COMPLETE STOP. At the very end of the night I got a small about of red blood but after one wipe that was it. Today I barely have any bleeding? It only comes in spots when I look at my panty liner but when I wipe there is a super small and very light tint of pink. Now that the night is coming to a close I now have nothing? Only a dull ache in my back and earlier I felt like a small oval thing that felt very soft but weird. Was that my uterus shifting for the baby? I haven’t been to the doctor. And I don’t know is o should. But I am alarmed.