What Causes Abdominal Cramps And Dark Clumpy Blood Discharge?

I am on the pill cerezette. I have a feeling of bloating lower cramp. now and again I have a clump of jelly like black blood followed by very light brown blood barely noticable. I haven't had a proper period in over a year is this normal? I recently went for a screening and my doctor said there were abnormal cells in my vagine but nothing to worry about. should I be worried? thanks becky