i don't have any advice - just empathy! my dd is also 4 months old and still waking up to eat in the middle of the night. between taking care of her and working 10 hour days when i go to work 3 days a week, i'm chronically exhausted. i try to work out in the evenings on my days at home when my husband can watch her, but i definitely have trouble finding the energy. i strive to work out for an hour, but i'm happy if i can get 30 minutes in. and forget about eating right! my diet is horrible because i grab what i can when i can. it usually has to be something i can fix in one minute or less, eat with one hand, or eat quickly. cooking is not an option right now. i'm trying to be patient and tell myself that eventually my dd will become more self sufficient and be able to entertain herself for longer periods.
hang in there! hopefully it will get easier and hopefully you'll start getting more sleep!
carrie