Need help on diagnosis for a patient suffering from lower abdominal pain for the past 10 years

I have a male 45-year-old patient suffering with lower left abdominal pain that has left him bedridden for multiple years at a time. I have been working with him for the past one and a half years at least three times a week.

We have been finally able to reduce the problem down to obliques. But I need help with proper diagnosis and treatment protocol.

He reports severe pain in his left lower abdominal area (around the obliques away from the rectus abdominis) when I asked him to do leg raises (Even 2-3 times) while sitting and squeeze the abdomen a little bit. He reports pain in the pelvic region most prominently inside the rectum.

However, he can do 30+ SLR at a time. He is also able to do. He is also able to do high knees indicating that psoas perhaps is not at fault. He is also able to do mountain climbers. Initially, when he came to me, he was mostly bedridden and was not able to do all of these exercises. But sitting and doing the leg raises creates intense pain for him even now.

His work up looks good. Abdominal MRI is okay. And so is MRI of the back and pelvis. He has also done a abdominal ultrasound as well is transrectal ultrasound. He has also seen gastroenterologist without any finding. From his 10 year medical history, it seems that there is no underlying problem with the visceral organs. he has also had a lumbar sympathetic nerve block done without any effect. He is not suffering from any other visible mental or physical disorder, apart from comorbid depression and anxiety when he was bedridden.

10 years ago the precipitating event was accidentally lifting a 3 kg weight while he was also having recurrent anal fissures. The most recent episode started two years ago when he again lifted a 4 kg weight.

What other tests can I do for a better differential diagnosis? And what kind of modified exercises can I prescribed for strengthening is obliques, assuming that is the source of the pain

Thanks for any inputs.