@Ian J might well be right. Have a think about why you are running your own business and whether it's been driven by positive thoughts and feelings or whether it was a suck it and see type venture without too much thought.
On the other hand... I, like many of us, have doubts on a day basis - it's entirely normal. I think I've said this a few times on this forum but you need to do what makes you happy. If running your own business doesn't, don't do it. If working for a particular boss doesn't, leave them. But consider that not all bosses are equal, some are great and give you a real purpose in life and in your role. What is the purpose of your business? Not what product or service are you selling, but why did you start it in the first place?
When I have a rough patch I think of the million and one benefits I get from running my own business. I get freedom, I answer to nobody, I don't have to do one thing over and over, i decide my hours, pay and who I work with. It's unpredictable but also rewarding. I have to depend on myself to deliver something or achieve a certain goal - this is rewarding in its own right. I don't care about the salary (although I do earn something from what I do). I've had a job paying nearly 10x as much working for an idiot - I would never go back to that, or a version of it, for any money!
Stop what you are doing. Try and remember why you are doing what you are doing, what's the purpose? You're not alone in your thinking, we all get there at times, just recognise that you will have fewer choices if you allow this negative mindset to continue.
Have a think. Free from pressurising yourself to make a decision right that second. It might take some time. It's tough right now, and will get tougher, but to me this is exactly the time that being ones own boss brings the biggest challenges and also the biggest satisfaction.
If you want to call and chat (I don't want money or gifts), I'm happy to do so...
Otherwise good luck, and remember, you're not alone!