Due to the enlarged subclavius muscle, your costoclavicular space is likely very tightly compressed. You are likely heading for a rib resection if PT or injections cannot help (the subclavius is resected as part of the rib resection procedure). You need to find the right PT as some PT can actually make matters worse.

I had issues with my subclavius and nothing (therapy or scalene block) was able to lower the first rib and open the costoclavicular space. Have you already tried a scalene block or botox? You can get a subclavius block in addition to the scalene block. These are usually done by a neurologist with ultrasound guidance.

I would seek out a therapist with experiencing in evaluating and treating rib disfunction (subluxation, torsion, etc). If you can't find a physiotherapist that knows ribs you may have to go to a chiropractor. Get all of your ribs checked and treated, not just the 1st.