K.K.
I feel you pain. I was a SAHM with a 2 yr old boy when I was preggers with my daughter. Sad to say, that whole pregnancy I just felt like a bump on a log. No motivation...just sorta sat around. I had probably 1 month during the 2nd trimester when I felt good and had energy. Things were much better after she was born.
Now I am preggers with my 3rd. The first trimester was typical...blah with no energy. However, by about 14 weeks I was feeling better. I am now 21 weeks and still feeling fairly good. Some days I still take an easy day and sit around, but much better then before. I have lowered my expectations of myself...I think that helps. I just do what I feel like doing, and try not to feel bad. I think you just have to accept that with each new addition...you have less time for the house stuff. And that's ok! It happens to all of us!
Good luck and hang in there!