You had a baby 6 weeks ago (Congrats!!!). Don't you think this could be part of the issue? He feels jealous and put out and is expressing his feelings by pretending he doesn't care about you and your reactions.
Ime little boys who put up a façade of "I don't care" always care enormously.
What he needs is a mum who is bigger than all that, who sees through it, who doesn't rise to the bait. The correct answer to "I don't love you" is "that doesn't matter, because I love you and I will always love you". Show him that, and you will be fine.
Try not to get too stuck into a rut of punishment. A lot of the time it is possible to manage behaviour without a set scale of punishment, often you can to stop undesirable behaviour simply by a firm NO, and then move on. And after all, if this does the trick- why not? job done. He will still learn the same lesson, i, e. that you are in charge.
If you do punish, then the punishment itself should be enough, not his reaction. Rules should be clear and consistent with specific offences leading to punishment. Not getting upset enough is not an offence and should not be treated as such. Otherwise you could find yourself getting into a vicious circle where you have to push harder and harder to break him. And if he is a proud and spirited little boy, that could go on for far too long.
Make sure you have extra 1-1 time, even if that does mean letting baby wait a little bit longer to be seen to, or your dh/a relative/a friend looking after baby. When the 3 of you are together, make sure your attention is focused on the elder one for a lot of the time: he is the one that is going to notice the most.
Don't let him see that you are hurt or upset by anything he does. When he is feeling vulnerable, the last thing he needs is to feel responsible for your emotions. Discipline him when he is naughty, but don't let him feel it is his job to keep you happy. That will only frighten him and make him more obdurate.