Hi Sheila:
Thanks for your pin oak question! Unfortunately, I'm not sure how helpful I'm going to be in answering your question since these kinds of questions frequently require an in-person site visit for proper evaluation. Therefore, your best bet is to get in contact with your local Univ. of Tennessee Extension office: https://www.uthort.com/
General questions I have are:
Is your newly planted tree receiving adequate sunlight? Pin oaks are shade intolerant, meaning they require plenty of direct sun.
Is the soil pH conducive to planting a pin oak? Pin oaks require acidic soils otherwise they develop chlorosis.
Did you consistently water the tree the first couple years and do you still water the tree during periods of inadequate precipitation?
Was the root system moist and healthy when the tree was planted? If not, that may be part of the issue.
Was the root ball of the tree planted at the proper depth, i.e., not too deep and not too shallow? Too deep or too shallow can cause root development issues.
Did you tease-apart the roots when you planted the tree to ensure it would not get "root bound"?
