the underwriter is questioning my income on my schedule C
So if you don't have a registered business, that means you have a sole proprietorship business. A sole proprietorship is not required to be registered or to have an EIN if the business has no employees. The only requirement is that you report the income on your tax return. What exactly is your business that you report income and expenses for on SCH C? What specific questions is the underwriter asking?
what is the UW questioning? Is he saying the numbers don't make sense or what? As Carl has stated the only form for an unincorporated single owner business is a Schedule C which is the profit and loss. if the UW is looking for a different form or reporting all i can say is there are many stupid UW's out there. you may need to talk to his boss.
Most likely they want a P & L ( and probably your business bank account statements) for the business showing your income to date since you do not have a W-2 ... they have to verify your income in some way ... and you DO have a business. They may also want proof that you actually made the income you reported on the Sch C as well as supporting docs for any expenses claimed ... again to verify you have an income to support your ability to payback the loan.
FYI ... a P&L is easy to produce if you keep proper records OR you use a bookkeeping program. To put one together manually is simple ... it is basically just your income and expenses listed like it shows up on the Sch C to show either a profit or loss for the year to date.