I am a 17-year-old female and i am experiencing an extremely painful strain in both feet every time i exercise. i tried switching shoes and loosening the laces but it doesn't make a difference. how can this be? is there a problem with my feet?

I would expect there is. When standing still, half your weight is placed on each foot. Walking shifts up to your full weight/foot. Running creates momentum & can place up to 6X your weight on each foot. If the added weight triggered by your exercises triggers pain, there is something wrong with your feet or foot-ware that exercise brings out. See your doc or podiatrist.

Strongly recommend a podiatry or orthopedic evaluation. You may have heel spurs, tarsal tunnel syndrome, or "plantar fasciitis". Have noted benefits with custom designed orthotics, and would suggest considering as a potential approach.

Agree with Dr. Mechanic. It is not feasible to provide a meaningful opinion without additional history, physical examination and may be some tests. It would be prudent to see a doctor or a podiatrist. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol, weed or street drugs.