Started Bleeding After Finger Insertion In Vagina. Why Did That Happen?

Less than a week ago my boyfriend was fingering me and i started to bleed , i had no pain or anything and only realised when he pointed it out to me. We do this on a regular basis but i ve never bled before, although it had been the first time in more than a month. I m not a virgin and It s nowhere near my period so thats not the conclusion. Since that night i ve had a very uncomfortable feeling down there and theres been blood or a browny blood in my knickers. Could you tell me what this is, and why it s happening ? Concerned.