Help !?

So I have had some dark brown bleeding today and a little tiny bit yesterday but it's very light. I had protected sex 3 days ago. I'm not supposed to get my period for like 2 and a half more weeks and my cycle is very regular. I have had cramps today and light bleeding but it's dark dark blood. I haven't been to the doctors in about two years. I need to find one, I know. But is this normal to bleed 3 days after intercourse and so dark of a color ?? I never have bled after sex before and it's not a new partner. So why do you think I'm bleeding now ?? We didn't try anything new or anything new either. Just had sex like we always have and now I'm bleeding ! Help ?!