Herniated L5-S1 Disc, mild arthritis, and Piriformis Syndrome

Hi everyone,

A long story incoming so apologies in advance, but I would appreciate some views from those who've either had similar experiences or professionals that have experience of treating people with the following if possible please...

I am 33 years of age, just over 11 stone, and I believe physically fit.
I work in IT, and sit mainly at a desk for 7.5 hours a day, with regular breaks.
My normal exercise routine pre first national lockdown back in March 2020, consisted of 20 minute body-weight HIIT sessions in lunch breaks 2-3 times a week, and 5km-10km runs 2-3 times a week.

However in the last 6 months, with working from home becoming the norm, I increased my running distances up to between 8-12 miles per run, and with a lack of a proper desk setup and physical movement being less than it normally would be whilst working, I have been suffering with what was at first lower back pain, to then having pain in the top right buttock, which eventually following an 8 mile run in May, moved into the entire of my right leg, leading to temporary numbness.

Following that run, I could no longer do any exercise due to weakness in the entire right leg, and sharp pain in the top right buttock, with pain increasing going up or down stairs/inclines, or bending and lifting my 4 year old. I can't fully explain what it feels like in the right leg, but when at its worst, the leg itself feels like it is 'holding on' if that makes sense, with sharp pain I can only associate with a twinged nerve.

I initially waited a few weeks for pain to resolve, but this did not happen and subsequently had a number of physiotherapy sessions between June-August, consisting of deep tissue massage in the affected buttock, with subsequent training plans designed to increase strength in the buttock and core areas. She stated it was likely to be piriformis syndrome but I felt like I didn't get a 100% positive diagnosis - I guess it is difficult to give this without scans.

In the midst of the physiotherapy, in July, I decided to go private to see a renowned spinal surgeon, at which point I had X-Ray and MRI scans done on my back. My work pay for my private care so I thought why not, hopefully it would put my mind at ease in terms of any spinal issues, and my older brother had seen the surgeon previously and was very complimentary as were all the reviews I had read about him.

The MRI showed a small disc herniation in the L5-S1 region, as well as mild arthritis which the surgeon told me was pretty normal for my age. The surgeon didn't believe in surgery and preferred a trial and error approach before going anywhere near that road.
I mentioned the physiotherapy and likely piriformis syndrome diagnosis, and he stated that piriformis syndrome is banded around too much in diagnosing of patients and that in all the years he had been performing surgery he had only seen real piriformis syndrome once, on an elderly woman following a hip replacement.

That said, I felt like the physio was helping me, so I continued for a few more sessions, carried on doing the strength exercise sessions twice a day, and was eventually pain free by the end of August, being able to do 5km runs without issue. I told the spinal surgeon that it was helping and he agreed probably best to continue with that approach, increase core strength and try to increase physical exercise and see how the body copes.
The physio booked me in for a follow up 4 weeks later but said feel free to cancel if the pain had not returned and I felt well.

By the time the appointment came around I was back running at least twice a week, able to do body-weight HIIT sessions, and felt well so cancelled the appointment. I was also discharged from the spinal surgeon at the same time.

Literally a week later, sods law, the pain returned but on a lesser scale than before. So I stopped running again, replaced it with walking, carried on with my core/buttock strength exercise routines and since then, on and off the pain has been there.

I have since then been able to do some running sessions, but not in any sort of routine because of the pain, and mainly at 5km distance, with a couple of 10km runs in there too.
This last week though, the pain has returned to the point it was at before, and I am at a loss to know whether to go back to physio since it helped before, or go back to the spinal surgeon and have an injection in the disc area itself (which is designed to reduce the size of the disc from memory of our conversation).

I don't feel like the core strength exercises are helping much anymore, and any heavy lifting (of which I've had to do a lot with the impending house move) exacerbating my pain.

I'd really appreciate some advice/guidance on this, since I am struggling to know what to do, or who to go to to be perfectly honest.