Ok, this thread doesn't have many messages and the OP seems to be a first timer? So I am hesitating to post but you never know, this might just help.
There is a huge difference between shouting at kids, which we all do when we are stressed, and calling them names. These aren't just names either, these are designed to inflict the most amount of hurt onto your ds, to make him feel worthless and stupid and unloved. Perhaps you are doing this because that is exactly how you feel yourself?
But what will happen is that your ds will honestly feel unloved. He will start to act up all the time because negative attention is all he is used to. Instead of being nice for cuddles, he will be naughty and will be called all kinds of horrible names again. That's just how he will think it works.
You need to get help. Start with your GP and ask for anger management and counselling. You obviously are very stressed (half term is always stressful) and may feel isolated and worthless yourself. You can only love others once you learn to love yourself.
Your ds is behaving exactly like any other little 5yo boy. You need to learn how to deal with his occasionally naughtyness without resorting to this. You need a plan. Therefore your next move should be to contact the Parent Support Adviser through the school. I am assuming your ds is at school.
You do not have to tell school why you want to see the PSA and they should not ask. I have seen mine because my ds was having anxiety problems. They are there to help support parents and everything you say to them is in confidence. Most PSAs run courses called Positive Parenting. I cannot recommend these courses highly enough. You get to meet a group of parents who are all experiencing problems with their children and with their parenting. It's not just a support group but it actually offers practical help that WORKS! Once you have a plan in place, you feel under control. You have a step by step solution that works no matter what the situation; whether he refuses to eat or refuses to go to bed or has a full-on tantrum in the supermarket, you will find yourself armed with a plan of what to do. This makes a huge difference.
The course also teaches you how to interact with your children in order to boost their confidence and encourage good behaviour. Personally I think every parent should attend such a course as it's just so very useful and it really does bring the parent back into control of the situation. You sound like you are losing control so this course would be right up your street.
You recognise that you have a problem. You know it is unacceptable and I'm telling you that your ds WILL be permanently damaged if you do not get help.
So, go to your GP. Again, you don't have to fully confide in him/her. Just say that you are finding things difficult, that you are having issues with anger and feelings of worthlessness and that you need to talk it through with someone.
Then ask the school to put you in touch with the Parent Support Adviser.
Other resources that can help are Family Lives, Relate for Parents and The Parent Support Service