What Causes Burning Sensation During Urination Post Intercourse?

What could this possibly be?
I have had sex with my partner several times, some a bit rough, for 3 days straight.
It was the first time in a very long time since we have had sexual intercourse.
From 3 days ago, I felt this sort of burning sensation during and after urination - sometimes I take painkillers and they work just fine, other times they don't.
I also have just a few drops of blood every time I pee, and just a small amount of it on the toilet paper.

I've seen that this could be an urinary tract infection... can there be any other possible causes?
It's been about 4 days now.. will it be too late if I go see a doctor tomorrow (5th day after symptoms)??