Implantation bleeding ba?

I have a PCOS, so I had my mens last Feb 4, 2022 and it ended last Feb 13. After that we had intercourse without any protection. In Feb 18, the night after we had intercourse, when I woke up there is a slight pink/red blood but after less than an hour it stopped. On Feb 22 & 25, I take a pt both came out negative. But I'm having mild cramps and lower back pain. #advicepls #pleasehelp