Sudden, severe pain for 20 years

Hi everyone. I'm a 24 year old female who has been suffering from sudden, severe shoulder pain (well, it's more in the angle of the chest and shoulder, sort of where the deltoid and pectoralis major muscles meet) for about 20 years. I was about 4-5 years old when I first noticed it. I never had any accidents/trauma. I ignored the pain for a long time (not sure why) until a few years ago when I got an MRI and it should a rotator cuff tear (which is not related to this pain-I get different aches in my arm related to that but in the actual shoulder area). The orthopedic surgeon I saw at the time didn't explain anything very well and said he didn't understand the sudden, crippling pain and to see a neurologist (which I never did). I recently saw another orthopedic surgeon, who says the pain is "coming from muscle" and to go to physical therapy.  Not sure I understand what he means by that. Recently, I stopped using the affected arm (even for basic things like holding light bags or lifting windows) and stopped sleeping on my right side, and a combo of those two has significantly decreased the frequency of these pains...but when I start using the arm, those pain come back. Which is why I'm scared to go to physical therapy-I get the pain upon exertion. And quite honestly, I'm not sure how physical therapy will help when we don't know why my muscle (s) is/are producing this pain. The pain usually lasts for a second, but sometimes it doesn't stop and all hell breaks loose. My first reaction is to immediately pour hot water over the area to make it stop. Was wondering if anyone could shed some insight, whether through personal or professional experience. Thanks for reading.