180 turn around on behavior

Question
My chihuahua over the past two weeks has really done a 180 with his behavior.  He is now 8 months old. My girlfriend and live together and both take care of him. Over the past 4-5 weeks he has become very aggressive, barking a lot, growling, snapping.  Sometimes there is nothing and no one around him when he does these things.  It was rare for him to even bark let alone snap at someone.  It is very confusing.

Answer
First,what could be a big help is if he's not neutered,getting him done will greatly reduce aggression,and 8 months is right around they become sexually mature,and is around the age when these types of problems pop up,so getting him done will be a big help

And secondly(and if he's been done)is to talk to a trainer as soon as possible,as this can become a VERY serious problem,even in a Chihuahua,and call up several trainers and tell the problems you are having with him,and go with the trainer that has the best answers over the phone-a trainer can show you steps on fixing problems like this,and this dog,right now is top dog,and training will put YOU in the top dog spot


Also,a big problem with small dogs is caused by carrying them,or babying them in general,do NOT carry the dog,even if it wants it-it is again putting him in the alpha spot,treat him like a dog.Also make him sit before feeding him,that also puts you in the alpha spot