I had my period on nov. 3rd-9th and had unprotected sex on the 13th and 15th. today (nov. 19th) i started spotting dark red/brownish . am i pregnant?

Too early to tell: The spotting is not related to being pregnant or not; that is probably a hormonal or stress reaction. If you are to ovulate as would be predicted based upon a 28 day cycle, you would be fertile on the 16th. Having sex on the 15th makes pregnancy a possibility but we won't know until you actually miss a period or do a test around that time.