First, make sure you're not combining depreciation and amortization. Depreciation is a reduction in cost basis, while amortization is a straight up deduction from taxable business income.
If you have a case where your expenses/depreciation exceed the business income, then once your taxable business income gets to zero, that's it. You can't deduct or depreciate any more. So if this is your case, any "unused" depreciation is carried over to the next year.
If you claimed less than 100% business use of a depreciable business asset, then that will also lower the amount of depreciation you are allowed.
