implantation bleeding or new birth control?

I had unprotected sex on Feb. 14th which was the last day of my period. He pulled out just before he came. I have been on birth control for over 3 years but just switched after my period to a different brand & dosage. I am experiencing random light brownish/pink spotting for the past day and my boobs have been extremely sore for like 2 weeks and i have had light cramping on and off for a couple days now. I am due for my period in 4 days. I have been taking my old birth control & this new one regularly at the same time everyday. Should I be concerned about being pregnant?