Hi Crystal,
I know how you feel. I was doing Rhythmic Step twice a week for about seven months before I was able to complete the whole workout, without modifications on a four inch step.
I was able to make it through the second aerobic segment (with modifications) after about 3 weeks, but it left me so darn tired and whipped that I had a hard time forcing myself to do the cool down and strech (obviously I was pushing myself a little to hard, we always demand so much more of ourselves than we would of others), all I wanted to do was plop down on the sofa.
After about seven months, I had just completed the second aerobic segment (without modifications) and realized, that yeah, I was feeling it, but I knew I could go on. I told myself I wouldn't force it, I would simply do what I could and just be happy that I had made some sort of progress. Believe it or not, I was actually able to finish the workout for the first time that day! O.k., I have to admit, I did push myself a little too much because during the Challenge segment I was dying, but you know how it is when you get so close to reaching a goal, sometimes you just throw caution to the wind and go for it.
But my long winded point is to just keep at it. It may not seem like it now, but your body is adapting and getting better with every workout!
Take care,
DeeDee