Lower back pain x 6 weeks. was 90% better 3 days ago but it's back. worst in am when first sitting up and when turning in bed. once up, however, the pain lessens about 80%. stiff to bend over but can do it. what could it be?

Most back pain is musculoskeletal - however given your age you probably have degeneration as well. PT is usually the initial treatment and if this does not get better see a Pain Specialist so that further workup can be done.

Although the most likely cause is presence of degenerative changes in vertebrae, and facets, might consider pain generator from sacroiliac joints, and even hips. Agree with physical therapy, and if too uncomfortable, could initiate via pool treatments. Might get some relief by wearing a sacroiliac belt at nighttime. Work with a physiatrist.