Do you do any other stroke? Drills? I am the queen of doing too much of one thing, currently going through labral tear, but I can tell you, and I am 63, long time masters swimmer, that trying to swim relaxed is one goal, also having someone look at your stroke and see if you are doing anything wrong that could be causing your issues. My neck hurts after a lot of backstroke, so I have to constantly remind myself to relax and keep head BACK, not tucked.
Pain is a sign to back off, and we don't want to hear it, but it's necessary. Don't give up. I'm not. I have had this tear for ten years!! I go hard, then I hurt, I stop, then back at it when the pain stops. I'm looking into stem cell procedures; I don't want surgery.
Chiropractic and massages are a good options, too. Hang in there.
Original Poster here: I stumbled upon a new therapy that has cured my shoulder impingement. Its simple too! Read Dr. John Kirsch book "Shoulder Pain?" - it's on amazon. All it involves is hanging and over time the shoulder space increases and the join is reformed with more room for tendons to move around. This has totally saved my love of swimming and I will continue to hang. I use weightlifting wrist straps to help me hang for longer. I do about 5 minutes a day and after 1 or 2 months I noticed big improvement in the water. Try it out! helps neck and back pain also.