Anyone else have this happen to them?

So I had gotten my menstrual cycle Friday the 20th. By Sunday my period was basically gone. My body was just getting rid of old blood at this point. It was the brownish color for 2 day & then completely gone by Tuesday. I had sex with my man for he’s birthday this past Thursday the 26th. Yesterday I start having really painful lower back aches to where I could barely move. Tonight I went to the bathroom and wiped and I was spotting. It was pink colored but now it’s light brown again.