Just started training - shoulder pain

Just started training for a sprint triathlon so doing around 1000m twice a week. Only been training 3 weeks and going well but left shoulder has started hurting today after swimming.

It’s the joint / front of shoulder.

If I give it a rest and reduce the volume should it recover? In my last coaching session he said my arms were coming around from the sides too much and I should lift elbow up more and kept arms closer in which I worked on. I wonder if that has irritated it or if it was my original poor form? Or maybe just the shock of doing all this swimming which my body isn’t used to.

I exercise a lot but not previously swimming.

Don’t want to pick up injuries etc that impact on my otherwise good progress