Your Doctor's advice is poor - 1000 calorie deficit per day is actually too much according to Govt. guidelines and the aim of aerobic exercise and calorie depletion is to lose fat, not go into catabolism (where muscle, as well as fat, is lost), which can happen if the calorie deficit is too high.
Aim for no more than 2lbs per week. For easy intro to aeobic, try a home mini trampoline (rebounder) and see how you get on. If you do no exercise just now, expecting you to suddenly burn 500 calories per day through exercise is alarming - exercise routines should be built up slowly and steadily for the non-active.