You could possibly be suffering from a Morton's neuroma - a benign 'tumor' on a nerve in your foot. In the truest sense, it is not a tumor but some thickening around the nerve. It is most commonly seen in people who are on their feet alot - and is more common in females. Check out this site for more specifics:
http://orthoinfo.aaos.org/fact/thr_r...pcategory=Foot
Also, there are stress fractures - actual small breaks in the bone - that can occur with repeated small injuries related to such activities as marching. Neither of these conditions are likely to get any better on their own. You need to be evaluated by a doctor (orthopedist) before it gets any worse...