That sort of thing always happens to me when I start a new medicine (ok, some are different). Things will be better for say 2-3 weeks maybe even 2 months and then I will slowly start to slide back down into the no energy zone. Usually when this happens my pdoc adjusts my meds or changes the med I'm on. I've also had my thyroid tested, but the test results didn't indicate anything that would make me tired.

Let us know what the pdoc says. I hate feeling exhausted all the time though, so I understand where you are coming from.