I need parenting advice! Please be polite-----

I am a single mother, almost 39 weeks pregnant, and I have a 5 year old who will be 6 in October. His dad isn't as strict as I am in his own home, but he respects his father's word much more than he does mine. I am struggling on getting my son to listen to me. Generally, he isn't a bad kid, but lately he has been fighting me when it comes to getting his way. If he wants to play a video game and I say no, he proceeds to speak over me, loudly, sometimes crying, asking why and pretty please, or will continuously ask me over and over again thinking his persistence is funny (something his father encourages.) His dad encourages him to also speak to me bluntly in ways a child should not speak to their mother. Like "hurry up mom." or "what's taking so long?" or "MOM, I SAID...." Well today's latest battle was over lunch. I made him a corndog and chopped up a few fresh strawberries (and even sprinkled it with sugar). He ate the corndog and then had a meltdown about the strawberries. He says his dad doesn't make him eat them and he doesn't like them and just had a complete meltdown. I told him he could either eat the strawberries and finish watching his movie when he was done, or he could skip the strawberries and go straight to bed. He sits at the table for 30 minutes and didn't eat them, asking me why I'm making him eat them and he doesn't want to, etc. I finally make him get down, go potty, and get in bed. He then proceeded to start screaming and crying and kicking the wall and his bed, high pitched screeching into his pillow. Repeating over and over again that he wants a movie, and then starts on and on about how he's hungry. Numerous commands to stop behaving that way, shut his mouth and close his eyes, an open palm swat on the butt and a pop to the mouth and he still wouldn't stop. I finally had to pull out the belt and give him two swats on the side of his leg. I hate resorting to that and it makes me feel so bad. He doesn't have any marks and I didn't hurt him but I can't have him throwing fits like this and disrespecting me, especially with the new baby on the way. So I guess what I'm asking is are there any other women struggling with this and are there any other ways to handle it that you could suggest? He's generally a good kid but he's really struggling with the issues between his dad and mines parenting and I see it more and more the more independent he gets. 😰