A big part is getting used to it. At the beginning I felt like throwing up after 2-3 sets of squats and fell asleep when coming home. Now I feel “fine” after 5 sets and don’t fall asleep at home.

Food can also play a role. Some people like training on empty stomachs and eating after, I like eating before.

Go to the doctor. Especially if you are in otherwise OK shape and your capacity for exercise doesn’t seem to improve with practice. Being unable to walk for one hour without severe fatigue is pretty good evidence of exercise intolerance.

Exercise intolerance is basically an inability to perform physical activities that someone your age typically would be able to.

This can be evidence of various underlying health issues (heart, lungs, muscle disorders, nutritional deficiencies).