I'm constantly itching and having a rash under my apron. I've lost over 100 pounds from gastric bypass in 2005. Back pain.

Thank you for your question and congratulations on your weight loss after surgery!  Unfortunately the hanging apron of skin that can develop with this degree of weight loss can be debilitating for patients.  Depending on an in-person examination as well as a review of your current medical condition you may be a candidate for removal through either a panniculectomy or tummy-tuck procedure.  I would recommend seeing a board certified plastic surgeon in consultation, they can offer you the best treatment options.  

The excessive tissue that you have can be treated with a body contouring procedure to remove the excess. This would help with the rash and most likely help with your back pain as well. It would require a formal consultation to make sure you were an appropriate candidate. Good luck.