You say you use a progressive system, and get the progress in weight, but don't have it in 1RM? I think you could try to add reps or sets too especially when the weight gets heavy. It will be hard at some point to go from 3x5 to 3x5 when there's even a little extra resistance involved. Like first doing 3x3 then 3x4 or 5x3, and slowly progress to 3x5, then get more weight. It's good to train with lower intensities and start slow and easy so to speak, but eventually it would be preferrable to atleast visit the more max effort zone of 80-90% of your 1RM.
Just one question remains. I noticed you said something about your long period of non-training. How consistent are you with your training? Is it like on-off training, or have you really been going to the gym and busting balls to the walls constantly for two years?
Yeah milk get's you some protein and carbs, that's good. Some calsium and vitamins as well. Like Stu said, get more carbo-loaded vegetables and fruits after working out.
Find out what bodybuilders do. We have some here, but the mainstream here is powerlifting, and that won't get you the right advice.
But he's looking to improve his three major lifts(bench, deadlift and squat) and increase strenght. He doesn't care much for getting lean or cut or hyperthrophy in general. Isn't that more of a powerlifter approach? I mean, what bodybuilder would say it's okay to have some fat and that I want to get stronger on my thee big meet lifts.