Spotting hours after sex?

So I've had no problems with bleeding or spotting this whole pregnancy I'm 36 weeks ,then me and my husband had sex and I had some spotting.. the weird part was it wasn't immediately following the sex. Everything was normal for a couple hours besides some extra watery discharge and then to my suprise like 3 or 4 hours later I had some pink/red spotting. What could it be?? It wasn't my mucus plug