Why am I not sore the second week of P90X?

It's normal, your body's just adjusting. Protien and other suppliments are there to enhance your results and also help repair your muscle tissue so it doesn't break down, but no, you won't have the same body as you do currently. Any excersise is going to make a difference. The more, the better. You really should consider adding some protien at least, it will make a big difference. Same with the yoga, but if you choose to skip that, at least do some intense stretching after your workout. This will keep you from getting too sore as well as help your muscles from getting too tight.