I know how you feel, I used to start work a 8am and sometimes I'd still be in the workshop till 3am. I'm not prying but I am going to try and help but I need some info; PM me if you prefere.
What do you do? Might sound simple but do you restore, just service and repairs etc.
Right outgoings.
Rent and what kind of location are you in. Is this a prime spot or are you tucked away.
Size of workshop, do you use all of the space?
rates
What insurance's have you got and what are they costing you?
elec, water gas etc.
What are you charging per hour?
Are you charging book time?
Are you marking your parts up? if so what %
What motors are you running and how many?
Have you got anyone working for you?
That should be a start but when your own your own its hard work.
I've been self employed for 5 years in the motor trade.