Hi Sue! I am in my 11th week and what you are going through is exactly what I went through--my energy level to workout was so limited and I would get so frustrated that I couldn't work out to the level I was accustomed to. Basically, I just decided to listen to my body and not to worry if I wasn't getting in my 5 to 6 workouts per week. I aimed for 3 workouts and focused on walking, low impact videos, and some light strenghth training (for some reason I had NO energy or motivation to ANY strength training!) I think the walking really helped alot and I also think it helped that I stopped putting pressure on myself to workout everyday. Everyone kept telling me that once I moved out of my first trimester, my energy levels would return and I would probably be able to workout more. Well, I am here to tell you the good news--this past week has been wonderful for me--On Sunday, I did Karen Voight's Strong and Smooth Moves; Monday I was able to do Cardiokicks (with modifications), and Tuesday I was able to do MIS (I used lighter weights than usual.) I took Wed off (though I'm sure I could have hopped on the treadmill!)
So, hang in there--remind yourself that feeling this way is for a limited time (hopefully!) and modify, modify, modify! At first I had a VERY hard time modifying--I just did not want to do it--I felt like I was cheating on my workouts and I was so annoyed that I just couldn't do it. But, after some trial and error and practicing those modifications, I have truly come to see the value of modifying and that it does not take away from your workout. I am going to try MIC tonight with modifications (change all high impact moves to low impact; eliminate plyos) and I can honestly say that I think this is doable and that I will still enjoy and benefit from the workout!
Sorry, I am rambling...but wanted you to not be down on yourself for not being motivated to workout, it is OKAY to take a break and I think during your pregnancy it is critical to listen to your body. Good luck!