Potty training difficulties

My son will be 3 in November and last weekend we started potty training. However he seems so stressed out about the process. When he needs a wee he gets himself all uptight, holds it for as long as possible and then doesn’t want to sit on the potty. He has only done 1 wee on the potty in 4 days. He is the same at nursery. We have tried rewards, stickers, choosing his own pants, distractions whilst sitting on the potty, but none of seems to be working. I now don’t know whether we pause for a few weeks or if we should continue. Has anyone experienced similar?