Why is my dog getting bald patches?

My dog is just under 5 months old and he is healthy and happy, he is 3/4 staff 1/4 lab and he is starting to get bald patches :S He doesn't have a rash or anything and he still seems happy, he dose not itch, there not in places were he can bite his fur out, he has 1 on his snout, 1 on top of his chest, and looks like he is starting to get one come up behind his ear, Does anyone know what is causing this? i took him to see the vet but could only see the nurse as do not get paid until friday, and i don't think she had a clue what she was on about as she said it might be mites, and recommended me an all in one dog protector solution which i am all ready using :S i told her this but then she told me it will take 3months 2 work, but i have been using for 2months already and they are getting worse surly this is not rite? it didn't help her being foreign and not understanding properly, if anyone could help would be so grateful as wanna help my lil man out asap if not will just have to wait for friday poor boy, thanks for your time guys