eat more greens like broccoli and spinnish. These contain iron which is essential in the production of red blood cells which carry oxygen to different parts of your body ive had the same problem i didnt have enough iron and felt tired all the time now i have extreame stamina and can last without sleep for longer When you have less oxygen there is less of a reaction in your muscles and cells. Oxygen + Glucose= Carbondioxide + water + energy The more glucose and oxygen you have the more energy you have as sypol as that. I do biologie so i know my stuff lol