I get tired very quickly and my form falls apart.
This tells me your weight is too heavy or you're fighting the bow (not fitted to you) and/or form.
Address the target. Stand straight up, feet straight down from your shoulders (more like arm pits). Head up, look to the target and draw bow and you as do try to keep the pin on the target (a little high is good as you can come down easier than go up). The bow comes to you, not you going to the bow. Peep should be right there, not tilting the head (a little exception if you're wanting nose/string contact).
Hints; If you can't keep the pin reasonably about the target while drawing you're draw weight is too heavy. If a solid (not forced, but repeatable) anchor the nose/string contact is not necessary. you and the bow are to be One.