Needs clinical examination. Most of the times MRI will show disc degeneration in asymptomatic people also .

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Left low back pain is due to your sitting and lying habits for work and recreational purposes where you may be tilted to the left. This lifestyle leads to shortening and tightness of muscles on that side with loss of flexibility. When you do any movements then these tight muscles get stretched and give pain. Because of pain you tend to remain in the same posture as it gives comfort but you end up increasing the muscle shortening. IMHO, MRI is just suggestive of degeneration and is not the cause of pain.

Disc work like shock absorbers and give flexibility. Your L5/S1 disc has lost its flexibility causing back pain and is swollen and pressing the nerve.

Early disc degeneration is there , pls consult to know more on how to manage