For me, If i'm working on a progression and my hand starts to hurt I'll take a 10-20 min break. Repeat ect. ect. till I can do it for a long period of time without the pain. Than on to the next one. I think it's normal as long as the pain isn't consistently their long after you take a break. Also keep your picking hand relaxed. I jacked my hand up a bit by having my right hand tensed up while picking it took about 5 days of no playing or puter to recover :(