Brief Answer:
Left L4-L5 disc herniation.

Detailed Answer:
I read your question carefully and I am sorry about the issues that you are experiencing.

I viewed both those MRI images. They both have similar findings, a herniated disc at the L4-L5 level with narrowing of the left foramina (which in turn leads to nerve compression and the symptoms you describe).
Narrowing is present on both MRIs, actually it is even more marked in the second MRI in my opinion, so if they are pre and post surgery it is true that the surgery has failed, there is new disc material herniating and compressing the nerve root.

There is a mild protrusion at L5-S1 level as well, but it leads to no narrowing or compression, shouldn't be causing any symptoms.

I remain at your disposal for further question.

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Brief Answer:
Another surgical procedure might be considered.

Detailed Answer:
I suppose since it's been some time you must already have tried non invasive measure like physical therapy, anti-inflammatory medication (like Ibuprofen, Naproxen etc) or other over the counter painkillers, neuropathic pain medication (gabapentin, pregabalin, amitriptyline, duloxetine etc).

So what is left now are invasive methods such as local injections with steroids and analgesics which may help the symptoms for some time, or re-address the disc with by having surgery again. Failed back surgery is not that uncommon, as surgery removes only a small fragment of the disc and it is well possible there to be other fragments herniating subsequently which can be addressed through another surgery.

I hope to have been of help.

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