I have a 3 month old and i have a couple of questions??

Ok. my baby boy is three and a half months old. for the last couple of days he has been cranky. He has been drooling more than usual and he has rosy red cheeks. is it possible for him to be teething so young? my second question is about frozen milk that has been in my frezeer for about 2 and a half months. I took some out to thaw and noticed it had freezer burn. It smells and tastes fine. Can i still use it or should i throw it out.