I don't know what you mean by discomfort so I can't say much anything about what to do for your arm.
One of the most important things to do is to work back into throwing very gradually after a break. Typically, after time off your arm has formed some scar tissue and tightened up. It is quite vulnerable then as a result. Start out throwing only about 30' for a few days and then work up to full distance at about 30' a week increase until you get to 150' of so then play it by feel to see how much your arm feels like improving. If you feel a twinge while throwing, as opposed to normal post throwing soreness then take a day or two off and go back down 1 step in distance.
If your arm continues to hurt and you can't progress in distance without pain, go see a doctor.
You should also make sure you warm up properly before throwing which should include as a minimum some running and preferably some arm circles and band exercises.