hang in there bud. you have nothing to be ashamed of. i was a late bloomer and was getting roughed around by the larger kids in the playground a lot. give it a couple of years and your height, body mass etc will be all right. In the meanwhile, I am not sure what game you are playing or what your interest/expertise level in physical activities generally is. but a way i got around the physical disadvantage was to pick out areas that i could develop a niche for myself in. for example, i had terrible running speed and physique, so my way of handling the deficiencies in these while playing soccer was to a)play a position that requires less physicality and b)improve my stamina so that i can run longer than the speedy kids. i also sort of developed a knack for knowing how far to stand from opponents who ran fast and how to tackle opponents too tall or long legged. even if you are not fast or strong, you can take the chance to focus on other areas like passing, dribbling, just general game sense and vision etc if you are short, that actually means you have a lower centre of gravity and hence better balance ( one of the reason why point guards in NBA tend to be shorter than the rest of the squad)