Hello and thankyou for approaching DoctorSpring with your query.
I have gone through your case and understand your concern.
Lower back pain can be due to a muscle pain or skeletal pain or as a result of nerve compression.
In order to help you better, please can you answer a few questions so that we can evaluate the cause of your pain.
1) Does the pain radiate to your thigh and leg?
2) Do you feel any numbness, tingling or shooting sensation in your leg?
3) Does any particular posture or activity worsen it?
4) Have you been treated for your ulcer and is it better now?

In addition to the above questions, the first thing you will require to get is an XRay of your lumbosacral spine to diagnose the cause.
If you already got an X-Ray or MRI done earlier, please can you tell me what were the findings.

Please reply as a follow up and I will guide you accordingly.
Thankyou