Completely exhausted

Hey all...we are expecting twins in Jan. I'm going to be 14wks on Monday..I am beyond exhausted. I have no energy, no motivation, and just feel like a sluggish bum..We already have 2 children 7 and 4 and they obviously keep me busy... I just have no desire to clean my house or basically move off the couch..help!! When does nesting kick in? I didn't really get it with my other 2...Is anyone else feeling this way? Shortness of breath normal after doing minimal cleaning? I vacuumed and did a load of laundry and I had to sit again.. uugghhh