Do you take any medication? They are notorious for side effects like exhaustion. Let us know about that also.
Since you have been severely fatigued for a while. Now you have to juggle getting back in shape. Your muscle tone has been somewhat lost. So you need to start getting it back, a little bit every day. Don't overdo it. Start with 100 steps and see how you feel the next day. If okay, then double it, but split into two sessions. Add 100 steps every day if you feel good from the previous days exercise. Keep us posted as to how that goes.
Tired after eating ..... your body is busy digesting. Paradoxically, that is the best time to do your walking. It helps you digest, gets your inner organs working.
I spent a number of years on a drug that killed my energy. Could not even sit up some days. So I know a little of where you are coming from.
TV still overstimulates me. We turn off the TV early, my husband uses ear phones after that. Going out with other people means I won't be able to sleep for hours.
The energy comes back slowly. It's not a magic pill. Patience is required.
Try to follow sleep hygiene above ........ not easy I know only too well. Get your Sleepyhead reports up and let the experts here help you tune in your settings. And stick within it. With time and effort you will be glad you did.