Trouble when sketching

When I animate, I like to do really fast sketches before I start on the lines. These are usually done in really quick strokes, but lately I've had a bit of an issue with it. Whenever I try to sketch like normal, I can only do one line and then I have to wait until it smooths. If I do it with my mouse its fine, and my tablet still works like usual in photoshop. I haven't found any sort of help for this, so any advice would be greatly appreciated.

I have a wacom intuos tablet, and I run on a mac.