Many of us have had similar experiences when starting a new sport. It takes a while for your muscles to adapt to the new workload of track practice. It can also take a while to adapt your muscles to new shoes. If it’s a real physical injury, or just “growing pains,” it would still be classified as a repetitive-motion injury.
I will share with you one insight from my own running, and from my training to treat sports injuries. Competitive running can be very hard on the muscles of the calf when they are not used to the workload. An interesting thing that happens, is when the muscles on the back of your lower leg become so strong and stiff, that the muscles on the front of the calf, which are smaller and weaker, have a hard time flexing against the stronger rear calf muscles as your feet and legs go through each foot strike.
Pushing forward when you run involves Plantarflexion, and returning the foot back up for another go is called Dorsiflexion. The plantarflexing muscles (Gastrocnemius and Soleus) train up to speed more quickly than the dorsiflexing muscles (chiefly Tibialis Anterior). The Tib A can swell from fighting the stronger rear muscles, producing a very painful form of shin splints.
However, another condition can occur when muscles are rapidly trained that you want to be particularly concerned about. It is called Compartment Syndrome. This painful condition results when the muscles grow faster than the sheathing around them (compartmental fascia) can stretch to accommodate this growth. The result can be quite painful, and may even cause circulation in the leg to cut off. The condition can require surgery or other invasive procedures to release the pressure.
For that reason, you should bring this condition to the attention of your school physician and of course, your parents. It may only be the growing pains I described earlier, but numbness can be a sign of excess pressure on the nerves or circulatory system in your legs, and warrants your immediate attention.
Good luck with your training, and thanks for bringing this to the attention of other runners in time to prevent further injury. My experience with this problem when I was running track, took several weeks to get over, but you may be luckier. Whatever you do, don’t simply try to run through it!