Hello I had gone through your question diligently and I will try to help you out in best possible way Looking at your description that could be hemorrhoids or fissure in anus Since you are overweight but you have reduced a lot I would advise you to reduce further if you can with dietary restrictions and regular physical exercises You have a family history of cancer, So to be on safe side I would advise you to consult your doctor for per rectal examination and an colonscopy if need be. Meanwhile try to avoid constipation by taking laxatives or stool softening agents like liquid paraffin or lactulose Lignocaine ointment for pain and burning sensation Pantoprazole or rabeprazole as an antiacidity medicines Have lots of fruits and vegetables with dietary fibers Hope this helps you wish you good health.