What Causes Brownish Vaginal Bleeding After Intercourse?

Hi I would like 2 know something,I finished my period round the 25 dec 2013 I had sex and the following week I had brown discharge for two days.. I never got my perion for Jan 2014 and we two weeks into the new month of feb 2014 I would like to know what is happening my breast is tender and I hav lower abdominel pains