Good luck, I think you're on the right track, congratulations on the job offer.
You may also want to think about pacing yourself, it is about prioritising what you HAVE to do in a week, planning when to do it and planning rest/recreation. Then you can gradually build up your activity or exercise over time. If your body is tired, there may be a reason that you have to pay attention. That doesn't mean take to your bed! That's a sure way to get weaker, but driving yourself into the ground may not be helpful either.
Have you checked out possible causes for tiredness with your doctor? It could be something simple like anaemia and easily treated.
I wish you all the best as you look for a way forward.