I want to lift more weight but i cant do it for some reason. I know that i am supposed to rest each muscle?

for at least a day before using it again. I have a schedule it goes like this... Mon, chest and abs. Tue, legs. Wed, biceps and back. Thur, rest. Fri, triceps and shoulders. Even though i follow this schedule and work very hard i am not lifting much more than i do right now. I can bench 200 with dumbells and 160 with bench press, whats up with that. what can i do besides a diet plan to lift more on the bench press? any suggestions please no wise cracks.