Case of a medium/large disappearing kidney stone?!

28 year old male, 85kg, 172cm. No recent changes in diet when symptoms started, minimal cancer risk factors. Drink socially, perhaps once or twice monthly. Not diabetic. No recurring medications other than finasteride and a multivitamin.

For the last 18 months, months I've experienced fatty/floating stools, bloating, persistent diffuse non-severe dull abdominal pain on the right side centered just under the right ribcage, and sometimes spreading to near the belly button (often continuous, not directly associated with eating). The pain often increases significantly with high impact exercise, increasing from a typical 1-3/10, sometimes to an 8/10 or more). I've also experienced frequent diarrhea (at least weekly), highly increased flatulence, frequent tachycardia after eating fatty foods (100-130bpm), poorly digested foods visible in stools, and frequent dizziness. Comprehensive blood work has been taken roughly every 3-4 months for the last year, with no significant abnormalities found.

This post relates only to the pain on the right side. I've now been through several ultrasounds and many other diagnostic tests, none of which found anything meaningful. After putting up with the continuing pain on the right side for the last 6 months with no new daignostics, and no lessening of the symptoms, I decided to go for another ultrasound.

The sonographer interpreting the results almost immediately told me on seeing my right kidney that I had a non-obstructive 6mm kidney stone, and that was likely the source of my pain. He seemed entirely certain of the diagnosis, and told me to follow up with a urologist.

I've attached imagery of the right kidney which he saw the kidney stone in here, along with his comments: https://imgur.com/a/iT3ndZr

Fast forward a month, and I went for another ultrasound at a separate clinic, being performed by consultant urologist. The consultant urologist concurred with the previous diagnosis by the sonographer, and said that I had a 7mm calculus in the right kidney. He sent me the same day to get a low-dose CT scan to identify the exact location of the kidney stone and its composition.

Fast forward another week, and he's emailed me the results of the CT scan, which are as follows:

""" Dear /u/Synchisis

We could not find a stone in the CT scan, maybe it was an artefact in the sonography.

It's unclear what's causing your pain. Maybe it's muscular after all.

I recommend a re-sonography here in approx.. 3-6 months.

Best regards """

I'm now at a loss as to what to think, as the symptoms are very much still present, and get significantly more painful when I attempt to run or perform any other high impact activity, to the point of stopping me from performing said activities (pain gets up to 8-9/10, enough to make me yell out sometimes). The pain is also not at all like a muscular pain. It's more internal, totally unaffected by most movements (unless they cause a lot of impact, repeatedly), and has not varied in intenisty or got worse or better in the last 18 months, despite me going to the gym and in general now having a much stronger body than I did 6-12 months ago. If the stone is an artefact of the sonography, how would it be picked up twice by two different doctors, using two different sets of equipment? It makes no sense at all to me.

I'm unsure as to what my next steps should be. Any advice or theories as to what might be going on would be most welcome.