Being less facetious, although this is nothing new:
I'm always amused by guys that say "I think my program has stopped working"
What's your program? (List of body parts)
What's your goal? "I want to get bigger."
1) Describe your program in more detail than chest/tri, back/bi, legs, shoulders.
What exercises, how many sets, how many reps, weight loading, etc. Help us help you.
2) Describe what, exactly, you ate yesterday. Be honest. Then tell us if that's a normal day.