You can do it, but next time you shoot, commit to working on it, not just flinging arrows. To start off, draw the bow without an arrow and hold for 10 seconds, it's important to feel your back holding the weight. Make sure your alignment is solid. Sometimes when we start shooting heavy weight we collapse inward which makes it difficult to hold the weight.
Next try doing the same with an arrow, only shoot after you reach 10, not at 10. What your are trying to do is build endurance and muscle memory and proper alignment. Work on it for a few sessions, I bet 55 won't be so bad.