If you can't lift weight, here's what you should do.

1. Run 3-4 miles a day..slow pace,fast pace it's ur choice but u have to run for that long..it's good if it's continuous.

2. Try swimming if u can't run..20 laps or more

3. Eat healthy food. NO FASTFOOD!!

4.Try eating more in ur breakfast and split your lunches...one at 12 and at 4.

5.Do not eat anything after 6 pm...except fruits and drink(water,juice,no sodas)

6.it's not neccesary to take supplements shake ect ect. You want protein, eat more food that contain most protein and drink a lot of milk.Remember some supplements are not FDA approved.
5.Do some fun sports on the wkend...soccer,cycling ect ect.

Hope this help.Gd luck!