You can sue. Or if you were divorced, you can have your divorce attorney file a motion to enforce the child support order.
Perhaps the best recourse is to elicit help from the Texas Attorney General's Child Support Division, for which you can find more information at the following web address:
The web address for the Texas Attorney General Child Support Division is:
The AG is certainly a way to go with your problem, especially if you are unable to afford an attorney. I believed an attorney is your best bet, however, to get things going quicker and keep them going. For "under the table" incomes, and attorney, in some cases, might be able to discover how much is being spent, which might be a better way to show his true income.