brush tool erratic and laggy

I've used photoshop CC for 2 years and I'm a little tired of my brush tool. I use it to sketch my outlines and I find once I do a reboot of my Mac and re-ster PS it works fine but a week or 2 later it starts to get laggy and erratic again, it won't draw smooth lines but tends to have a mind of it's own rather like a wonky shopping cart. 

Am I doing something wrong?