Self employed folks should keep good records of their income and expenses. Deposit all your income, including cash, into the business checking account. If you take credit, have that income go into the checking account. Pay all your business bills out of the business checking account. Have a separate account for your personal expenses. Pay yourself out of the business checking account with a check, and put that money into the personal account. Don't mix the two accounts. Pay business bills from the business account. Since you have access to a computer, get a software program called QuickBooks, to keep track of the business records. You will be able to show the court what your income and expenses are, and what you are paying yourself. Talk to a CPA to help you get ready to file tax returns and verify the income . Your records will have credibility if you follow these suggestions.
Since you are self-employed and deal in cash, it is difficult to prove, or disprove, any amount of income. So, you may be subject to some pretty probing discovery if the other parent does not believe what you produce. You could start with a profit and loss statement for the year to date, and with monthly detail. Bank statements, sales tax reports, 1099's, analysis of your expenses and lifestyle are all potential sources of information. You should consult with an experienced family law attorney. Good luck.
The above "answer" is for discussion purposes only and is neither intended as legal advice nor to create an attorney-client relationship. An attorney-client relationship is not created until after an in person consultation and I agree in writing to provide representation. I am licensed solely in the state of Arizona. You should consult with a knowledgeable attorney in your jurisdiction.