If you were following their routine to the T, your exercises would be changing every week anyway for the first few weeks. If you're just following the principles, check to make sure you're not hitting arms or tris super hard in some way on another day. And check your form. Most guys use way too narrow of a grip on bench, utilising the tris and setting themselves up for injury. If you're not sure where your grip should be, just ask someone who looks like they know what they're doing on bench, most will be glad to give you a few tips. My arms are really long and I used a narrow grip for a long time before figuring out it needed to be wider... like wider than the rings wide.
Also make sure your shoulder blades are squeezed together, your whole body is tight, and you have arch in your back. Do not let the weight deviate from it's course. It should come down to the very bottom of your chest without you having to correct the path, and your push should feel like you are actually pushing up and down a little bit instead of just straight up. Bench form really takes a while to get used to.
Also try going down to maybe 2 or 3 super duper intense heavy reps for ~3 sets/exercise (remember, around 8 sets TOTAL for chest using max OT). You should almost, but not quite, need a spot for the last one. Very low reps can help your strength plateau break. And if all else fails, skip chest for a week and come back to it. Your arms or chest may simply need some time to repair.
edit: oh, I forgot. Eat some more too