Well, DEFINATELY warm up good before your workout. Other than that, I guess your body is just getting used to the motions of the exercises. But, if the pain continues, go see a doctor about it. You may have calcium deficiency or something wrong with your joints. Not to scare anyone but it is quite common. But I doubt that you have that, maybe just getting used to the exercises. Or they are overloaded as well. Just be careful and don't injure yourself.