Hi!
I think it's entirely possible that he is just acting out his insecurities and frustration. Is it possible to get him into a doggie day care a couple of times a week so that he can interact and play with some other dogs? Boo (he's 10 lbs also) sometimes gets grumpy and I've started doing date night with him. Just the two of us go someplace and spend some time together and then stop by Wendys and split a cheeseburger on the way home. What's a date without a dinner, right.
Good luck, I'm sure others will have more suggestions. Oh, and post some pictures of your boy when you can.