First how old are you? Depending by your age it could be just your body changing. dark brown blood means that you are bleeding slowly. If it was bright red it would mean you are bleeding fast. If you are going thru cramps as well I would suggest to put a tampon in and soak in as hot of water as you can stand. Sometimes it could be a clot stuck in there and hot water even a hot water bottle will disolve it. hot that helps.