Newly Agressive Lab

Question
My Lab-mix has become very agressive,even toward me and I am the one that takes care of him. He had a flea allergy and I took him to the vet and he gave him a shot, I bought dip and I put stuff down his back to prevent fleas. Well we came home and I babhed him in flea and tick shampoo, put dip on him and that stuff down his back, this is what the vet told me to do. I can do almost anything to him except when I give him a toy and ask him to bring it to me, he growles at me and he is very serious,no tail waging to kind looks. He seems like two dogs in one, a kind and loving dog and an aggressive bad dog. I try very hard to take good care of him, he has been nutered,had shots and lots of treats and love. I love him soo much and I do not want to get rid of him, I can't hardly stand to think about that. We had a lawnmower stole,close to his pen, while we were on a trip, could he have a problem with that? The cats get in his pen and agitates him,could that be it? I don't know what to do , can you please help me? He has snapped at several people and tried to bite others,he has even snapped at my poodle, recently.
He comes in the house some and I don't know, I am giving him fish oil, could that do anything to him? Can you help me please?He is 1 year and 9 mo. old.His name is Bubba and he weighs 72.3 lbs.
Thanks
Linda

Answer
Did you discuss the aggression with the vet?  It is hard to be even tempered when you itch.  Perhaps he will be better as the flea treatment has time to take effect.

He could be maturing and starting to challenge you for leadership.  You listed several responsible ways you are caring for him, but not obedience training.  
Having a good pack structure reduces such problems.  The dogs see all the
people and dogs in the household as a pack with each having their own rank in
the pack and a top dog.  Life is much easier if the 2 legged pack members
outrank the 4 legged ones.  You can learn to play the role of top dog by
reading some books or going to a good obedience class. A good obedience class
or book is about you being top dog, not about rewarding standard commands with
a treat. Start at http://www.dogsbestfriend.com/