Hi Ishen7! Firt of all Apart from physical thérapist, am also podiatrist, and maybe i can offer you another point of view and try to add new solutions to your problem.
As i have understood from your review, youve been doing stretchings to rule out that the musculature supports the difference in length, working also with foot arch but no work, isn't it?
The functional difference of length in legs is caused by many factors. The main of them is a greater pronation of one subastragaline joint comparing it with the other. Sometimes is caused by a congenital shorten-member, that can only be treated (non surgery) with foot orthosis. Depending on the cause, the orthosis would have diferent pieces. (Either a Medial Heel Skyve or a Rise to level the sacrum and relieve the pain.
I hope I've helped you. Any other question, please send a private.