What Causes Yellow Vaginal Discharge After Sexual Intercourse?

I had sex with someone I have been seeing on and off for about 3 years last Thursday. There was fresh blood on the sheets after he came out of me. We had unprotected sex. My vagina seems to smell a bit more than usual and I have a slight yellowy discharge. Should I go and see a doctor? Do you know if anything could be wrong? I am 47.