Playing the guitar is a physical feat, and it is only natural that the growing pains are to follow.

The best advice I can give is to take it slow, and don't over do it. Once you have started to feel some pain, stop for the day. The worst thing you can do is work through it and that will only make it worse down the road.

Dealing with discomfort is unfortunately something that will continue to happen throughout your career. About every 2 years I go through a stint where I have step away for a bit to let my hand get back to normal.

Focus also on your posture while you play and practice. That is equally as important as well.