i agree with dylan, sounds like a form problem. next time you shoot try this. forget about hitting the bulseye. draw back and think about the position of your sholder. is it pushing up toward your ear? your sholder blade is it pushing backwards? think of the tension of each muscle. now let your breath out and let your sholder drop and relax as much as posible. is your grip tense? it too should be relaxed. only enough presure to keep the bow from falling. the best advise i was given when i started was "practice does not make perfect only perfect practice does" if you practice bad habits in form your body will remember this and contenue to shoot improperly. practice your form every shot if you get the least bit tired stop shooting, if you dont it will make bad habits.
good luck and shoot strait
Ron