How long will my lower back hurt after spinal tap? cant hardly set back.

Up to several days: It can persist several days. Watch out for progressive pain, fever, weakness in your legs or incontinence as these may be signs of post-procedure bleeding or infection. Back pain is fairly common after a lumbar puncture 10-25 % and should resolve over the subsequent 3-7 days. If not you should be evaluated by a medical provider.