You'll always get sore if you push yourself hard enough. I'm somewhat of a newbie too. Started riding about a year ago. I stopped getting sore after rides several months ago. Then two weeks ago I tried my first ride with the A group which just about killed me. I was sore the next day.
For the miles you're doing, I'd say a normal healthy diet is fine. When you start doing 1,000 miles/month then you'll probably need to adjust your diet. I ride about 400 miles/month and just eat like normal.