Greetings Jenny:
Tree pest/disease questions are likened to calling your medical professional and asking him/her what is ailing you -- the most common answer you are going to hear is that you need to come in for a doctors appointment (i.e., you need to have a professional arborist/forester/horticulturalist examine your tree on-site).
More than likely, your tree is just going through "transplanting shock". Transplanting shock commonly occurs during the first couple years of tree planting -- new tree, reduced root system, temperature and moisture extremes, etc. You need to monitor the soil moisture around your newly planted tree -- too much water is just as bad as too little water!
Too much urine from your dog can significantly affect the soil pH around this newly planted tree -- I strongly recommend that you encourage your dog to conduct his business elsewhere in the yard :-)