Fresh air, sunshine, healthy foods, and exercise, are the things needed to grow. I do not know where you live or if you have a place to get medical care. If you are worried talk to your parent or guardian. Maybe they can take you to visit your Dr or health department, but remember people come in all shapes and sizes. You are within normal limits for a 12 yr old. You probably will be having another growth spurt very soon. Until then, eat the healthiest food you can, drink clean water, and make sure and get fresh air and exercise every day. Don't worry about your size compared to other kids. We all have different growth patterns too. Also, if you have internet, look up yoga. There are several ways to stretch and lengthen the muscles. It can also make you stronger. Just don't over do it. You can't force your body to grow, but you can strengthen what you already have. Good luck!