Thats not a program, thats a list of bodyparts and days of the week. What exercises do you do? How many sets? What rep range? Hows is this program periodized (if at all)? Right now thats not enough info to go on.
I will say right now that rest is probably more important than training - you don't grow when you're working out in the gym, you grow when you're vegging out on the couch stuffing your face with food. You'll stall pretty quick if you aren't taking regular rest days. One day rest to every workout day in a week is a good rule of thumb. Any less than three rest days a week is seriously pushing it.
Its not about muscles. Your muscles don't regulate their own individual growth. Growth happens as an overall systemic response by your body as a unit. If you tire out that unit your performance will drop.
Take more rest.
But yeah, post up more info because thats all i can do with what you've provided, lol.