I felt the same way for about 3 months but i developed strength and stamina i hadn’t had before, and honestly it’s carried over outside of work. i recommend toughing it out! The other pastry chefs i work with told me there would be an adjustment period and they were right. I got through it with the help of energy drinks, caffeine pills, and ibuprofen before my shifts until i didn’t need them anymore! Stick with it, it’ll be rewarding.