Sigh, 6 years old. LOL They are knuckleheads at that age. They DO ask a lot of questions but what you are describing is a persistent child. He'd like you to change his answer. I went to a parenting class and they said something that really hit home for me. Kids hear our answer but they don't understand it. So, as they get older, they are like "well, that doesn't make sense so I'm doing X (not what parents said)." So, what about explaining. You can only take 5 toys because . . . (room in car, hard to keep up with) and put in something that would matter to him such as if we take more than 5 toys, it will be easier to lose one and then you'd miss that when we have to go back home without it. Sometimes we just say NO because we said so but kids do want to know why. Anyway, I'd look at his persistence as a good trait overall. That is a key personality trait that helps in life. But also, make sure you never change your answer as in letting him wear you down.
Also, they say goofy things. You don't love me. I love cartoons more than you. That's all the nonsense that kids of that age will say from time to time. He wants a reaction from you. Just say "okay" and move on. Don't punish him or make a huge deal out of it in my opinion. Unless he is calling you a name or something which is against the rules of your house. One thing I do with my kids (when they were little and now) is we have a rule that they can think whatever they want. Anything. Even that they hate me! But they can't say everything they think. It's called a filter. :>)
Now I have read things about strep causing emotional changes in kids. It's just that your son doesn't sound too out of the ordinary to me. He's testing the waters and boundaries a bit. That's normal in my opinion. good luck
A couple of questions if you don't mind. Does he do the same thing at school? Specifically ask his teacher. If he does it in both places, then its more difficult to deal with then just one place.
And, do you have any younger children at home? If so - how old are they?
These will help us help you (hopefully)