What Causes Thick And Brownish Vaginal Bleeding After Having Sex?

Hi I came on my period New Year's Day. This last for 10 days. It then stopped. I had sexual intercourse and my period started again. Know I am spotting which is thick and brownish so need to wear a pad. My periods have always been irregular and have had spotting before. I have had a smear which was fine. Should I go back to my doctor. Feed up feeling bloated and having back pain.?