Some of your programming is a bit strange as it recruits the same msucles as a primary actuator more than once throughout the week. Let me give some examples:

Week 1:
Dumbell Press - Pectoralis Major
Bench Press - Pectoralis Major

Week 3:
Close Pushup - Pectoralis Major

Week 1:
Pushups - Triceps

Week 3:
Skullcrushers - Triceps

You may be running into plateaus because various muscle groups are fatigued later in the week. Try to limit your programming to two muscle groups/day. For example, my programming is:

DAY 1:
Legs (Quads, hamstring, soleus, gastrocnemius, gluts)
Stomach (Abdominal and obliques)

DAY 2:
Chest (Pectoralis major, pectoralis minor, serratus)
Shoulder (Anterior/posterior/lateral delt)

DAY 3:
Back (Lats, traps, Iliac crest, fascia)
Arms (Everything in the fore arm, bicep)

In no instance does a muscle group get recruited as the primary actuator twice in one week. Like I said, that just leads to muscle fatigue. You must do what works for you, but I suggest switching around your routine to isolate the muscle groups in some way similar to what I outlined.

You can drop pushups completely, as if you're doing bench, they're more effective.

I would get rid of preacher curls and move up to 8 bodyweight dips, then switch to weighted dips. Preachers are an isolation exercise and not terribly prudent for beginners like us who still benefit greatly from the amazing compound exercise that is the dip.

I also notice that you have no focus on your arms aside from what impact is created by pullups and bench. I would move to eliminate pullups and add DB curls to your programming. Retain pullups as they're amazing.

I would advise dropping back extensions in favor of deadlifts as, again, hyperextensions are another isolation exercise. Deadlifts will focus your back but also give you intensity in your abdomen and legs.

While you have flat bench on your rotation, your pectoralis minor is being ignored. I would add incline bench to the rotation to make sure you're getting even development in your chest area.

Drop crunches and replace them with weighted incline situps and romanian situps. Your abs will die in a fiery death, and it'll be great.

For arnold press, replace it with DB shoulder press and keep your lateral raises above shoulder level. You'll receive adequate delt work from these two exercises, plus using the bar will increase your intensity and intermuscular recruitment.

Lastly, you may simply have stalled. You may need to do what's called a reset where you go back to a lighter weight and slowly work yourself back up to your plateau. It's also a bit psychological, as admitting you're at a plateau has the tendency to reinforce it. Grab that ****ing weight and beat the **** out of it!