Sour Muscles

My stomach muscles hate me right now. I never knew I had so many of them and how easy it was to get them aggravate. They are screaming at me to stop working out. Ever since starting this weight loss program from work, I've started doing Pilates. That involves one of those big balls and then rolling the ball in front of you while still hanging on to it. It's about 10 times more muscles building than situps. At least with situps, I would gradually get my stomach muscles mad at me, rather than instantly mad at me like I've done with the Pilates.