Dogwood is an understory lower canopy tree that preffers shade to dappled sunlight so you should consider planting a companion tree that will outgrow it in height & provide shade to the south east of it. You can also build a seasonal little shade for it with 4 poles, some garden twine & shade cloth to shade it from the sun. Place it directly over the tree or create a little wall of shade cloth to the south east where the midday sun sits around 3pm. If it is sunbaked make sure to give it extra water to make it through the hot part of the day. I would plan to build a more permanent trellis or wall as a sun shade with wood slats or lattice if it will live there long term. If it doesn't improve, something else could be wrong like a pest or disease.