Are you on any medication that might affect your energy levels?
Could you get things like your thyroid, blood sugar and iron levels checked?
It could be something as simple as a deficiency. There are other conditions that have fatigue as a symptom including MH issues so there really are lots of things that it could be.
The best thing is to get it checked out though, as you will then be able to address it.
You should definitely be able to exercise for an hour a day without feeling too fatigued though, assuming you have a healthy diet and get enough sleep.