Weird Spotting

I noticed light brown spotting in my panties when I woke up this morning. No more than a spoon full. I put on a panty liner and noticed another spoon full a few hours later. I am experiencing dull cramping, nothing too painful. My long time SO and I have been having unprotected sex for at least the past year (both in love and have no STDs, planning on marriage). This spotting is occurring about 11 DPO. We had sex on my fertile day, but used the withdraw method twice. I am not due for AF for another 4-5 days and I have very regular 29 day cycles. What are your thoughts? Possible pregnancy? Something else?