Feeling very sleepy and tired is not something you will be able to avoid when your body needs to heal. I have gone through the same myself, and after much experimentation, I never found a cure. The only thing you can do is just keep at it, get plenty of rest and sleep, keep stress levels down, and then you’ll start getting your energy back throughout the entire day.
Unless you’re simply starving at those points of the day you are feeling most sleepy. You could try eating more before or around this time of day to see if it makes a difference. A snack of some kind, perhaps.