You may be spotting during sex because your boyfriend (or husband or whoever) is irritating your cervix slightly.
Discharge is not a sign of pregnancy. Discharge changes from cycle to cycle, day to day. For some women it changes drastically, for others not so much. If you suspect you are pregnant, you should take a pregnancy test 14 days after the time you had sex which you believe you got pregnant from.
However, if you are taking your birth control correctly, chances of being pregnant are very low.