orthotics

Orthotics do not impair your performance - and yes you can wear them in your spikes (but depending upon how bulky the orthotics are you might have to get a new pair.)

However, IMHO I don't think orthotics are a very good long term solution. I wore them for years for pronation - and first starting having problems when I was sprinting/soccer at your age. Then I found that the problem originated not in my body, but in the comfy/cushy training shoes I had been wearing more or less constantly, which had 1. atrophied all the tiny muscles in the feet and lower leg, and 2. encouraged poor running/walking habits and form (particularly over striding and "heel striking".)

This is why many athletes now do at least some training barefoot, both to stengthen their feet/lower legs (which improves your sprinting and prevent injuries/pronation) and to improve form. This is also the reasoning behind Vibram Five Fingers. Wearing these is like running barefoot, but with a sort of glove on. A very neat product, highly recommended, I use them everyday: www.vibramfivefingers.com

Of course, barefeet on grass works out well too. Some people now run barefoot on almost any surface.

You might want to check out:

www.runningbarefoot.org

www.posetech.com