What Causes Severe Constipation Along With Numbness In Anal Region?

my 18 year old son hasn't had a bowel movement in about 5 weeks. been to three different hospital er in last two weeks. xrays show hes ful. however they say no blockages and no obstructions. my son has tried everything for constipation over the counter as well as four or five prescribed. my son says he cant feel anything down there anymore. hes lost about 15lbs in the past two weeks or so. hes also had a seizure like episode a week ago. ERs say its no emergency. however,to not have a bowel movement in 5 weeks has to be deadly!!! my son feels as if hes dying. any suggestions would be very appreciated. thank u a concerned mother