Took Plan B after unprotected sex, got period within 3 days, 2 weeks later spotting occurred and now it looks like the beginning of a lighter period--What's going on?

I had not gotten my period for over 2 months (May-most of July). I assume this is stress related. I had unprotected sex with boyfriend (monogamous relationship for over years) and immediately took Plan B on 7/19. Within 3 days, 7/22, I got my period--somewhat heavier flow; however, I believe my body was to go through its menstrual cycle regardless of Plan B. 2 weeks later, 8/5-8, I notice lighter brown discharge every other day, similar to the signs of when I start a normal period cycle. On 8/9-10, the brown discharge turned clear but had light spotting. Today, 8/11, there is slightly heavier spotting--no brown discharge. There are no other symptoms--esp. no back pains (which are my normal menstrual cycle symptoms) What is going on? Am I going through another menstrual cycle? Or is this the side effects of Plan B? Should I see a doctor? Please help.