Well, pink is discharge mixed with a little blood. Fresh blood (as brown discharge is old blood). That could be simply hormonal from the stopping of the BC pill. Or it can be irritation due to infection--- but with an infection, either fungal or bacterial, you'd have other symptoms. Yeast is common and you'd have itching most likely and discharge. Bacterial is accompanied by a strong and foul odor usually and thin greyish discharge. Any other symptoms besides the pink discharge? If you had unprotected sex though, you did risk pregnancy. It just doesn't show itself -- if you conceived-- immediately like that though. So, 2.5 weeks after you had the unprotected sex, take a pregnancy test. Get some condoms if you don't want to take the pill to protect yourself. But let me know if you have any other symptoms. good luck