How can I stop my son from throwing temper tantrums and so on?

He is 4 yrs old and has recently started acting out in a severe manner. He can be the sweetest child ever and so loving, yet at the same time there is times when I want to run into a closet and hide. For example today he decided he didn't want to go to his martial arts cl and proceeded to scream at me until I left only to calm down and beg to go back and I let him and he just started all over again. I think alot of his problem has to do with being told no. I have never had a problem sticking to the punishment I give whether it be taking cartoons or toys away even time outs. I have tried to ignore his behavior but that has proven to be impossible after relentless hours of screaming and him saying things such as I hate you, I can't love you and so on. It has started very recently but I cannot think of anything that has changed to cause this sort of reaction. I am at my wits end and finding myself about to meltdown several times a day. I love him to death but it hurts me I cannot figure out how to stop this. Any help would be appreciated, I do not believe in medicating children or taking them to a psychologist or so on. I just want to feel some control back in my life which I feel I have lost since the onset of this.