Low Energy Preggy Mom

Since I became pregnant (I'm 18 weeks now), I always feel tired and unmotivated. I used to be a passionate full time career woman with sidelines after office hours but now all I want to do (or I can do due to low energy) is to sleep, eat and do a little work during office hours. I really feel guilty about my state now and I also feel like a burden to others for being less productive/capable. Is there something I can do to improve my motivation and energy? Or this is just normal for pregnant women? Please give me advise. Thank you so much mommies..