4th pregnancy and pooped!

I'm on my 4th pregnancy and have 3 boys (10,5,2). I work full time, then come home and try to keep up with the kids.  I want to try and workout to feel better physically but I'm just so exhausted.  And I get so overwhelmed sometimes trying to keep up with everything. (For ex. I swept the floor and 1 hr later you can't even tell).  Not to mention I feel huge.  (My sister who is a stick is preggo with her 1st and has barely gained weight).  Does anyone else feel the same way?  Any suggestions or encouraging words?