Strange Behavior after Neutering

Question
Just recently we have had our 7 month old male collie cross neutered.  Since his operation, which went well, he has been exhibiting strange behavior.  All bad.  He has since totally forgotten any of his obedience training we have done with him.  He growls and sasses anytime we ask him to do anything, even sitting.  He has started showing more aggression towards everyone in the family.  He is barking, growling and nipping.  Which is odd since the neutering should calm that down.  We had asserted our dominance over the dog as we were told in doggy school.  Do we start all over again or could there be a medical problem we should be watching for?  He doesnt seem to be in any pain or any discomfort. Thank you for your time in advance.

Answer
A physical check up never hurts with a behavioral problem even without recent surgery.  Likely the neutering was too recent for all the hormones to be out of his system yet.  Even then, it is a big help, but no cure all.  This sounds like normal 7 month old behavior.  Likely he has most of his adult size, and no longer looks or feels like a puppy, think teenager.  His personality is largely determined by heredity and early socialization, 6 to 12 weeks being a very important time.  However, the personality is not fully mature until about 3 years.  He will test you and feel out your will to dominate.  Hold him to what your learned at doggy school. If that doesn't show some results in a week, come back and I will help with stronger methods.  An instant "Bad dog!" in a stern, but quiet voice in responce to the nipping and other problems may be all it takes.  Don't let him get away with the nipping.