Puppy tried to bite my older dog

I’d like to preface this post by saying we do have a professional trainer involved and he attends puppy classes. I’m just currently waiting to hear back from her and need to get this out.

We have had our 4 month old Aussie Shepherd puppy for 10 days. I researched the breed and breeder within an inch of my life. I wanted a high energy breed for walking and hiking etc.

The breeder is a professional shower and is registered with our national kennel club. His parents are vigorously health tested.

Within a few days of bringing our puppy home, I took him to the vets for a general check. He was TERRIFIED. He was shaking, I had to carry him everywhere and he growled at the vet. When on walks if there’s another dog or a person who flat out tries to bolt off, treats won’t change it, me picking him up doesn’t help. We are working with the trainer to slowly expose him to things and build up his confidence as this is not normal for a puppy his age.

This already feels overwhelming as I’m heart broken I don’t have a puppy I can do regular training with, EVERYTHING is about getting him confident.

Now, this morning he lunged and snapped at my 7 year old dogs face. I got him in time so I don’t know whether it was a warning snap or whether he actually tried to bite him but I am really upset. I was eating and I believe the puppy was resource guarding. My older dog wasn’t even close to him!

It’s now just another issue and I am really worried that I am out of my depth here and I’m going to end up with an incredibly reactive or aggressive dog.

Does anyone have any similar experience or advice?

Just to be clear. He is a very loving puppy and we adore him. Him and my dog eat separately ALWAYS. They are separated when given their kongs etc so there’s no need for the puppy to feel his food is threatened.