The third day is the worst.
As a Marine physical fitness is a way of life. I worked out and ran well before vaping and I knew that smoking was impacting performance in a huge way. Since starting vaping I've cut 3 mins off my 3 mile time and have broken, and keep on breaking personal records with kettlebells and weight training. I hit a big slump over the winter, no surprise that I was up from 1 PAD to 1.5 PAD during the same time. After kicking the cigs the slump was destroyed.
Keep at it with the P90X. "The third day is the worst" is just a saying for the third day of soreness. That will pass and soon you will no longer wake up sore, but refreshed and feeling ready for the next workout.