I'm a newbie too, but what if you tried eating meats with fat? Lean meat is yummy and all, but what if you tried eating something with more fat in it? That is going to be more calorie dense.
I've been a fan of lean meats for the longest time and eating meat with fat in it skeaves me out a little still. But, baby steps for me. I ate some duck on Christmas and it was yummy. Today I ate chicken skin and it was actually quite good. I was a little surprised.
Maybe make the leap to eating 100% primal and chuck out anything that isn't. That might be enough to take you to enough calories and also keeping you interested in eating primal food. And if you're not hungry, don't eat. I think that's one of the best parts of PB, if you're hungry, eat. If you're not, don't. No schedules or anything you need to stick to.
I don't know if that helps any, but I don't think you should stress about it. If you are feeling better and stronger and more vibrant, I think that is all the reason you'll need to stick with it.