Painter 2019 - brushes slow in responding

My brushes are getting slow to respond when switching them. Is there a reason why? A couple of days it was working fine, quick, and now it is slowing down. As for rotating my image, I work on a Mac, and using the short cut keys, and when I do, my image is slow to rotate, or very quickly and it is difficult to get it at the angle I want. Any specific reasons why this is happening> Thanks.