Front arm sinking on breath

Hi all, I did a TI workshop 6 weeks ago and went from swimming a couple of lengths front crawl (freestyle) to regularly swimming a mile, so stroke and enjoyment has been transformed.

I'm sure my stroke isn't fantastic, though, and in particular I find my leading (right) arm is sinking when I breathe to the left causing me to become unstable and rush the recovery. Any thoughts on where I might be going wrong or recommendations on how I can improve this?