I have terrible lower backpain when getting up from bed an when leaning over or lifting light things etc what causes it?

Varies . Varies, among the more common cause is an abnormal facet joint, which is often aggravated coming from a flexed to an extended position. There are other possibilities as well. I would not hesitate to be seen for an accurate diagnosis and to discuss treatment options.
Please see your PCP. "terrible" raises a red flag. This is best discussed with a provider asap. Most back pain is "mechanical" and not a huge problem-but you used the term "terrible", and though we men are wimps, it does worry me a bit. May i suggest a D.O. Who is trained in this area?
Back pain. The back pain you describe is most commonly caused by degeneration of your spine--things like herniated discs, "slipped discs, " muscle spasms, or instability. Less commonly, back pain can be due to scoliosis, tumors, fractures, or infections.