Explanation? I’m confused

Okay, So i ended my period near March 28, that was my last day so I have only been off my period about 2 weeks. Well, the last week i have had weird cramping in my hip and my stomach. And I couldn’t figure out why. Yesterday, I went to the restroom and wiped and there was blood. Not a lot, very thin, Just one wipe and gone type stuff. So I took a pregnancy test today, I was genuinely confused. And it’s negative. And tbh my fiancé and I have only Had sex once in these two weeks and he pulled out (YES! i know that is not a form of BC and not a hundred percent effective) , but any how Any explanation as to why this stuff is happening?