For you experienced lifters, I'm hoping you can help me figure out a couple things I've been experiencing:

Been lifting for the past six months. After rapid noob gains, I'm starting to plateau on the amount of weight I can consistently lift.

Question 1: What's the best way to break through a plateau?

Also, it's odd to me that some days I'm able to do all of my reps for all of my sets, but other days I'm not able to do all reps for all sets--and I'm using the same amount of weight, same number of sets, same number of reps. For example, one day I'll hit all my reps for all sets on bench, but a couple days later, or one day the following week, I'll be unable to do the same amount of reps and sets at the same weight. I have this expectation that I'm going to consistently progress, so it throws me for a loop when this happens. So . . .

Question 2: any idea why this sometimes happens?

I lift three days per week (M, W, F) religiously. I haven't missed a day of lifting in six months, and my consistency in lifting makes me feel like I ought to be getting more consistent progress than I am right now.