Brownish, reddish bleeding. What is it?

I had unprotected sex the 23rd, 24th and 25th day of my cycle, where he used the pull out method. My cycle is usually around 33 days. During one of those times he hit my cervix couple of times, and it hurt very very bad for two days.
On the 28th day of my cycle, I went to see a gynecologist for my yearly test, and to get birth control. She said it looked like my period was going to start that day. That day i started getting brownish, reddish spotting. Also that day I started taking my birth control pills. Its been three days of very light brownish, reddish spotting, which I thought at first was my period. It is not getting heavier though, so I am really starting to worry that this blood is not my regular period.

Anyone has any suggestions as to what this might be?