This muscle behind my shin and when I play soccer, I tightens up and bothers me. What is it called?

Magnesium strengthens muscles, calms nerves, stops cramps, and fights infections. Get epsom salt. It is cheap, five bux for a year's supply. Put a dose in a glass with water to cover and stir until it dissolves. Fill the glass with lemonade and drink it. You can take it without the lemonade but you won't like the taste. Milk of magnesia is more expensive but nicer tasting and gentler laxative action.

This is my first guess because magnesium deficiency is rather common among American youngsters. There are other possible causes, and more than one muscle there. You should study some books about nutrition so you can eat right.