Keep iron levels up, by eating green food or you can take iron supplement. But honestly its just a part of pregnancy, and that energy comes back in the 2nd tir-mester for most, then disappears again toward the end of the third :) Congrats by the way!
If you work out or just even go for walks. If you get your blood moving and pumping that will increase your adrenaline and in turn increase your energy.... it is completely normal to be tired during your first trimester though. If you go to babycenter.com they have a bunch of stuff on this. Plus you can get weekly up dates on what is happening with you and the baby... I love these!