Healthy Food Chart

Hello everyone,
I am 18, weigh 165 at 5'6'', and looking to lose 20 pounds. Only last year I weighed a healthy 135 and was very active in sports. However, recently I have been diagnosed with a medical condition and am restricted from running or other "high impact activities".

I have always eaten a healthy diet that consists of lots of fruits and vegetables, lean meat, and whole grains. For about a month, I have been walking about 6 days a week for 30 minutes at 4 mph. I don't understand what is impeding my weight loss. I was wondering if anyone could suggest "low impact activities" that will tone my body and help me lose weight, as it seems that my current regiment is not working.

Also, my medical condition might be slowing down my metabolism; so, is there any foods that naturally speed the metabolism? (I am not willing to use weight loss pills or fad diets).

Thank you!