Your poor thing. It's very common for us to feel like this sometimes.
This is how I felt for a period. Relentless is exactly the right word for it.
I used to wish the time away sometimes.
First the hard-talking part of my advice:
You must try and get out of the mindset that your children owe you anything. They literally did not ask to be born and they cannot change their behaviour without you changing your or your mindset.
IME Children are meanest to their parents, whom they love and feel safe with, however if you are particularly not coping or feeling very low and desperate, he may be picking up on that and acting out feelings he can't express.
Which brings me to the second part:
Are you getting enough help? Time alone? Emotional support?
You can't be strong for him if you don't have someone helping you in practical and emotional ways. If your mood is persistently low and you are getting angry or crying a lot, pr not sleeping, then you may need to see your GP
Are there any signs from school etc that he's not developing normally? How's his behaviour there?
How old is/are your other children?
The very worst time for me was when mine were 2 and 4 , and 3 and 5
Lots of questions, sorry.
Parenting is very hard. But you will look back and know you did your best.
Mine are teens now and I have enjoyed them more and more as they've got older.