I think this is less about being a mum and more about the split of parenting to be honest.
When you and DH are both at home things should be split equally (the parenting, the cooking, the tidying up, the cleaning).
Do you get out much without your DS? See friends in the evening / at weekends / go to the gym/whatever activities you are interested in? And I don’t mean that you go out and when you get back all the dirty dishes etc have been left for you to sort out and the house is chaos.
I’m assuming you work from home if you have a small business.. do you get much company from other adults? This is something I miss, working from home. Is going back to being employed an option?
Do you and your DH have an equal split of leisure time?
These are all questions that you should ask yourself and think about whether you are happy with the answer.
As a comparison, I have a 5yo and 2yo and have just been on a solo holiday for 5 days with friends. DH was fine with the kids while I was away.
Just to add… it’s never going to be perfect or totally back on track. But I think with just one it should start to feel easier and manageable at this age if your DH is pulling his weight.