What Causes Pain In Lower Abdomen Radiating To Thighs?

My fiancé has had a constant dull pain in his lower abdomen that radiates into both thighs for approx. a month. Recently he passed a fair amount of bright blood during one urination. He denies frequent urination, burning or painful urination or having passed further blood. The pain got some better after passing the blood but he continues to complain of abdominal and thigh pain. Could this be something other than a UTI? He says he has passed a stone in the past but the symptoms are not similar to what he feels now. Thank you.