Hello and welcome to DoctorSpring. I have read your question with diligence.
The symptoms you have described, fit the diagnosis of sacro iliac dysfunction. Sacro iliac dysfunction manifests as pain at the joint of the sacrum and ilium bones of the pelvis (which is around the lower back). It can be due to multiple causes but in your case it seems to have got precipitated by the excessive bending and probably walking.

In case of disc prolapse/ slip disc, the patient will present with pain on coughing and sneezing movements, unlike your case, and the pain may radiate to the leg. The pain is usually a pricking or burning kind of pain. If there is associated narrowing of the spinal canal, than that pain also increases on walking and relieves on rest.

Your symptoms are that of sacro iliac dysfunction. You can avoid it by avoiding excessive and abnormal bending movements at your back.
Take a mild analgesic drug with a muscle relaxant. Or an OTC drug Ibuprofen will help.
Continue with the warm water baths/ compresses. Visit a physiotherapist for appropriate exercises that will help your condition.

In case you feel no improvement in 2 weeks, you can visit an Orthopedician. He will have to do a physical examination on you and based on the findings will tell you what X-Rays are required.

Feel free to follow up with any further queries.
Thanks

Hello,

The mattresses should be firm enough to support the normal curves of our spine. There should not be any dents in mattresses.

I am sorry about physiotherapist part because I am not aware about your area.

With best wishes.