I am sorry to hear things are not fun.
Here are a couple of things parents I know have found work
Get a card of stickers, and every time your DS does something good give him or a special chart a sticker. Even little stuff like smiling at a sibling, following a simple direction you give etc.
The aim is not to reward the child but to get rid of your stickers in as short a time as possible. The first time it may take all day but if you try it a few times you'll get better at finding the positives.
This sort of turns the table on bad behaviour. It makes you look t the good things about your kid and if you explain your challenge you might even find your DS trying to help you get ride of your stickers......

The other idea is set an alarm to go off every 15 mins to 1/2 hr. Each time it bips you HAVE to write down a good thing your DS has done in that time. Even if all you can think of is "he didn't yell" or "He refrained from leaping on furniture". At the end of the day or even by lunch time read him all the good things you wrote ........
This can also help turn the tables and start to focus on the positive....
Good luck and I hope things improve