How do Myofascial Trigger Point injections work? I would appreciate input before I agree to it

56 years old, mild pain/stiffness in left side from bottom of ribcage to hip bone. Year and a half of discomfort, had to quit golf. Does not itch. No unusual medicines. In the last year, two MRIs, two CTs, two xrays, a colonoscopy and a full blood panel.

Nothing noted. I didn't want to find cancer or anything bad, but it's super frustrating not to find anything. This is an all-day long everyday condition.

They sent me to a GI doc and he dismissed me quickly, said it was not gastro. I would agree with that. Has nothing to do with what I eat, etc.

Anyone with experience with the MTP treatment, please let me know how that works