What are the options so I can help you
Exercise programs and sports activities can differ in number of participants from one person doing an activity like jogging or swimming, to hundreds of participants at a track meet. Structure can be loose in solo exercises where you can set your own pace, or be very strict in most competitive sports. Competition varies from none to highly competitive, and can be on an individual or team level. More complex sports and activities can present a high skill level.
A healthy eating habit and correct weight gain method.
Find motivation, possibly medication if it's serious, go see a doctor, do your favorite activities, talk to a trusted adult about it.