Lower back pain for about 4 months along with frequent urge to urinate. mri found min. protruding disc l5s1. no nerve compression. only pain sitting.

Herniated disc: At L5-S1, if the disc protrusion is large, it can compress and irritate L5 as well as S1 nerves causing pain to radiate down the leg (typical sciatica). If it is not pinching the nerves, you can get back pain while sitting as the disc gets more compressed while sitting esp leaning forward and slouching. Use a lumbar pillow and standup every 30 min and walk for 3 min every time. Avoid bending.

Urinary problems: Other causes of low back pain and frequent urination could include problems with the genitourinary system. It might help to chekc the kidneys/bladder with imagining techniques and testing if not allready done.

Possibly discogenic.: Sorry you are suffering from this...Your symptoms sound as if they may be from your disc protrusion at L5-S1. There are other possibilities. If your pain does not get better, if you develop shooting pain and numbness, weakness, or if you have bowel or bladder difficulty then you need a surgical evaluation, otherwise your primary care provider can help the back pain to improve +/- physical therapy.