I'd also recommend trying different blades in your razor. You've started with a great razor, but when it comes to blades, everyone's face is a little different. Derby Extra blades are a perfect example. I love them. They work pretty well for my face in a wide variety of razors. Just about half of the people that try them say they really don't like them, though. I think too often, rookies are too quick to "blame the equipment", but with DE blades, sometimes they are the right. Find another blade that is not quite as painful to learn with, then after a month or so come back and try the Derbys again.

The left side of my neck is always harder for me to get really smooth, so it would always be more irritated than the right side. It's just the way my beard grows. Until you've had some practice, give yourself permission to settle for a less than perfect shave. Just because you can run your hand against the grain an feel roughness, doesn't mean anyone else can see it. Do 2 passes and check the mirror. With lighter colored hair, you might even get away with 1 pass. After you've found some comfortable blades, had some practice, and your face has gotten used to this type of shaving, you'll be able to go 3 passes and get that Baby's Bottom Smooth shave.