What Does Light Brown Bleeding After Unprotected Sex Indicate?

Hello. I had my period on 29 December 2014 Had unprotected sex on 15,18, 24 this month. I had a light brown on 25 after using the toilet then yesterday in the afternoon I had a full bleeding today very light colour but very priky in the lower abdomen and I saw one big clot this evening. I have no period pains I usually have but rather prickly