Hi Im A Male 39 My Lower Back Pains Me

Hi im a male 39 my lower back pains me a lot and my joints hurt also at times I can't even go to wrk I pass blood in my stool from time to time what could be happening to me I went to c a doctor but he said I was OK but how can I be OK when the problems keep occurring when I was about 10 yrs old i had an accident where by I was crush by a vehicle could it be that