15weeks bleeding

I’m 15weeks today, yesterday I had sex around 5pm, fell asleep and peed around 11pm dark red toilet bowl & when I wiped everytime .. panicked and went to ER. Bleeding was very very light after within same hour.. Got an ultrasound and baby was PERFECT, 153bpm, growth was normal ...

Nurse said to follow up with OB of course but what the hell? They couldn’t even tell why I was bleeding bc everything was normal.

Ever happened to anyone before? Could it be due to the sex?