After sex i have been having red, pink and then brown discharge for 3 days. i should start my period in 2 days. could i be pregnant?

Could be: Your symptoms are not particularly suggestive of preg. Of course being sexually active makes pregnancy a possibility. Especially if unprotected. The easiest way to put your concerns to rest would be to get a preg test at the pharmacy. If its neg and your period is late, check it again in 5 days or go see you doctor. If the discharge continues for very long you might want to have it checked.

Best to do a home : pregnancy test. That's the most accurate. Good luck!