Fitness is divided into three stages: adaptation period, exercise period and consolidation period. I conclude that you belong to the adaptation period. Generally speaking, the adaptation period is about 6 weeks. In the meantime, we must persist. When you are tired, you can start light weight and low difficulty exercises. Don't rush for success. Just wait until your body gets used to it. Fitness is a long-term project. Only by adhering to fitness, developing good living habits and integrating fitness into our lives can we improve our physical fitness and make our lives happier. I am a personal trainer. I hope my answer is helpful to you.