Bleeding after period

Ive always been super regular. I had my period last week (normal.) When it stopped I had sex and my stomach wad hurting for 3 days. It felt like I pulled a muscle. Now I am bleeding again(had sex last night.) It is dark brown. No cramping or any "period signs." I called my dr but he hasn't called back. I stopped fertility medications in September and had 2 normal periods since. I was on clomid, trigger injections and estrogen. Any suggestions on what it could be?