Substitute fist swimming for your normal stroke. This takes the stress off your shoulder. Look on YouTube for Swimming fist drill
This is a great suggestion.
That after just increasing kicking 400 yards per day for 2 weeks
I would definitely NOT suddenly start kicking a lot
I did that based upon advice here ended up causing soreness in my knee. Bad enough I had to stop biking and running for 2 weeks
I’m sorry to hear that. Kicking has technique too. IDK if that was an issue for you. Adding that much kick - which isn’t a lot - and getting hurt from it is somewhat strange.