Welcome Lisa and Sparta! If you post some pictures we could take some guesses as to what he's mixed with

Lisa, I understand about your worrying about his weight.  He does look thin but his legs are long and you did indicate that he gets thin looking after each growth spurt. He is so cute, I can really see the corgi and his ears want to stand up but I don't think they will. I had an Elkhound/spaniel mix and her ears tried hard with with bottom half sorta straight. But the top never got up.  Back to the weight.  I like to give my dogs boiled eggs since they are so good nutritionally. Don't give him much carbohydrates as that just fattens them with out building muscle and strength.  You can give him vegetables and some chicken.  I even let mine have some apple and banana because I eat those in the morning and they stand around waiting.  I will see if I can find a recipe for some home made treats that I need to fix for my dogs.  It involves eggs, honey, peanut butter, whole wheat flow and some wheat germ.  You roll it thin and bake at about 400 and then let them dry to firm them some but I don't remember the exact amounts but I could make some and guess if you are interested.  I have buying a bunch of stuff and I think it often has components from China and I doubt the value.

Lois