Everyone has given fantastic suggestions so far. Try weeding out the possibility of a food allergy first. If not, you may need to take him to the vet to have him tested and make sure he isn't having an outbreak of demodex mange or some sort of pyoderma (skin infection). These things can happen if your dog is stressed or come on the heels of an allergic reaction and require veterinary attention to treat.
Also, as far as the licking on his wound are concerned... be careful. Large breed dogs and especially danes have a tendency to obsessivly lick small wounds, itchy spots, etc. Especially if they are stressed and can cause what are called lick granulomas and hot spots. If you are concerned at all you should contact your vet!
best of luck to you in your new adventure into the life of a Dane parent!!