Forearm and bicep? That sounds a little more involved than the usual tendinitis. Do you have any bruises visible? If so, could indicate a torn muscle. My guess is you've strained a tendon that attaches your forearm to your bicep, at the attachment areas.
Take 2/3 weeks off and baby it. Start with ice for a few days then start putting some heat on it and ease back into your disc golf activity very slowly. If the problem persists, either A) take months off to heal or B) go see a medical professional.