Missed period negative test

I had sex a month ago, the day my period ended unprotected. I get that I wasn’t ovulating so I thought nothing of it, well like 3 days after sex I randomly had pink blood when I wiped. It wasn’t old blood from my period because old blood turns brown... but I’m 3 days late on my period. I took a test last night and it came up weird. There was like 3 horizontal lines in the spot where it says your pregnant so I think it’s just a cheapo. Anyone get pregnant right after your period or got negative but was pregnant.