If your hand hurts after writing with a pen you're probably holding it wrong. There are a lot of complex biomechanics going on and very little attention is paid to building proper form any more. Proper form costs nothing beyond a little of your time training yourself out of whatever bad form you happen to have adopted.
The most common reason for your hand hurting after an extended writing session is a death grip on the writing tool; ideally you should be holding it just hard enough to put it where you want. Someone should be able to lean over your shoulder and snatch the tool from your hand with little resistance.
Also very common is putting weight on your wrist. Your whole arm should be a little bit active, carrying your hand around the page as you write or draw. Ideally your wrist is completely stiff; this does little for control, but it helps lower the chances of the tendons that control your fingers rubbing up against the bones of your wrist and deteriorating. You could get a wrist brace to help you practice this.
If you want more of this stuff you will find it in vintage "penmanship manuals", from the days when the most convenient method of writing was a fountain pen. I largely got it by word of mouth when I was working in animation next to old pros who routinely passed on their secrets of proper form as a way to help the new kids avoid career-ending wrist injuries from bad form.