I don't know how long it takes for Fentanyl to leave your body, but whatever addiction you have it takes a lot longer to leave the mind. A lot lot longer
As for having no energy, I'm on 90 days plus now and I still sit around at times with no ambition whatsoever to do anything. Just like when I was drinking. For me it's taking baby steps. When I do something I feel I have achieved something, even if it was really small. As long as the steps are forward, it doesn't matter how small they are.
But please listen to Dee's advise and see your doctor if you are at all concerned.