Any advise on chronic "morning only" lower back pain?

Every morning for the last 2 years I have been waking up with terrible lower back pain, to the point I am unable to lift my son from his crib without istance. It lasts general thru mid morning then seems to disappear only to reappear during the night hours and 1st thing in the morning. I have been to the chiropractor who took x-rays and said something about a disc but wanted to see me 5 x's a week, I went for about 4 weeks with no progress so I visited my MD who took another set of x-rays and said he saw nothing and recommended drugs. I have been sleeping with a pillow between my knees it used to help a little but not any more, I have also tried every different bed in my house so it's not the mattress. Any advise???????????