Lower back stiffness and pain

I've been having lower back pain for about 3 years now. It started as a nagging pain as I sat at my desk in work and now hurts constantly, again at fairly low level. I did get an mri done, which showed a degenerated disc at L4/5 which was bulging laterally to the right and had a tear in the location in the bulge.

The thing is, I don't think that this is the cause of my trouble, I don't have any leg pain at all for example. The pain seems to be centered near the SI joints, although these were found to be ok in the mri in terms of spacing. Also I have no additional pain during activities such as walking or even running.

A couple of physiotherapists have mentioned that I seem to have hardened tissue in SI joint area (mri mentions sclerosis superiorly to the SI joints). Certainly I can feel 'lumpiness' when i press on these areas and there is pain also. Just wondering if these could be muscle adhesions? I have always kept fit, doing weight training several times a week and also some cardio. I never did anything excessively but could my pain and stiffness be caused by muscle adhesions?

Any thoughts are welcome

chris