In that aspect you know more than many people two or three times your age. Now you've recovered from your illness and you have started to feel better. I see you're a bit worried about gaining too much weight. This is where we need to discuss healthy attitudes towards food and exercise. Food isn't the enemy.
Food is like nuclear energy.
If used responsibly it provides all the energy you need. If used irresponsibly it can wreack havoc. Exercise doesn't need to be miserable. It was tedious, rote, memorization. You were paying your dues.