bleeding/sex question

Hi, Let me 1st introduce myself.  DH & I are 32/31, married & TTC since January.  I spent 10+ yrs on BC (most recently NuvaRing).  My cycles are slowly becoming more normal (started at 45 days & now down to about 31).  I'm coming up with near +OPKs, but not yet one that was 100% for sure.  Yes, I know that I need to chart & I'm planning on it next cycle.
Question- DH & I BDed this AM & I immedately started a bright red flow that lasted almost all morning.  Now I have this dull ache/cramping feeling.    Any ideas on this?  It's never happened before. 
I have my annual exam next Friday, & I will talk to her about this.  But with a possible O coming up, I hope this doesn't cause a problem!!