As someone who started out only able to bench a little more than the bar five year ago and can now bench my own body weight, I can tell you that you need to two things:

1. Low reps, high weight.
2. Eat, eat, eat.

Since you're doing 3x5's of compound exercises, it sounds like you're doing something similar to Rippetoe's Starting Strength. Which is good. That system will add a lot of muscle and make you a lot stronger. I did it twice and both times I got a LOT stronger. I know Philip on this board mentioned getting great results from it too.

But you have to eat. If you're not gaining strength, you're not eating enough. Eat clean, but eat a lot. Lots of protein. Lots of veggies.

Right now I'm doing a modification of Rippetoe that takes into account the Reverse-Pyramid Training mentioned at http://www.leangains.com. My workouts are as follows (up until this week):

A = Squats/Bench/Rows
B = Deadlift/Military/Chin-Ups

I switched it up this week because doing heavy Squats/Deadlifts every other day started to hurt my lower back a lot. So now I rotate them a bit differently, replacing Squats with Leg Extensions/Curls once a week. But the idea is the same. Full body work outs doing big compound lifts. I've been adding a lot of muscle and strength since August. And the reason is I EAT. I eat like a goddamn horse.