K8, I was (am) exactly the same. I was waiting for this burst of energy in the second trimester but now I am at 33weeks I guess I should give up waiting.
Thankfully, tiredness has been the only ailment I have had - no sickness or anything else really, and just general aches and pains, but I have never been so tired in my life as I have being pregnant, and as warpig says, I have never slept so soundly.
If you feel tired then sleep, there is no harm in that atall, and make the most of it as you surely won't get much over the coming months! X