My dog is 9 years old what is wrong with her skin?

My dog is 9 years old she had flea pretty bad about a month ago. we treated her with front line plus . The fleas seem to be gone but she got a good size raw sore on the front of her neck about 3 weeks ago. that is all better now and the hair is growing back, But now she is starting to get a smaller raw crusty sore on the top of her head by her ear. looking over the back of he neck she has a butch of crusty bumps . her skin looks vary dry and flakey. and her hair falls out pretty easily. any idea what this could be. we thought it might be from the fleas but not sure now that the fleas are gone, she has never had anything like this befor but she is allergic to fleas and cheep food. we have to give her blue seal food or she will start to lose hair also. Please help.