Why is my cat showing negative behavior after being spayed?

My cat is 5-6 years old. I got her spayed because every time she went into heat, her symptoms became worse and more intolerable. Immediately after the procedure, she started showing signs of aggression towards family members and the dog which was never present previously. I called the vet and he said it was her way of dealing with the pain, so I waited for it to stop. It has been 5 months and her aggression hasn't ceased. She has also started fighting our other cat for its food and clawing into the bread at night. She licks A LOT more than she ever has (herself and people - kind of gross). My family is getting very tired of her antics. Before she was spayed, she was a normal, sweet cat. She cuddled, got along with the other pets, and didn't get into too much mischief (the most would be jumping on the counter to get to an open window). I need to know why all of these things are happening after her spay. Is it because I got her spayed late or from complications from the procedure? Any and all help is appreciated.