I am so worn out!!!

I don't know what is wrong with me, but the mornings that I get up and actually do something, I end up feeling like complete shit the rest of the day!!  Either I am really that out of shape or there is something wrong with me!!  We have been doing the water babies class twice a week and for the rest of the day, after the class, I am physically weak and just generally feel drained!!  Then this morning I went to my first water aerobics class and it was really neat, I felt great afterwards and was really excited about going more next week, but for the rest of today I have felt drained again!  I would of loved nothing more than to just lay in bed all day, but that isn't possible with Savannah, obviously!  I am going to continue to go to both of these things and hope that I start handling the rest of the day better!