Harris County has a very strong vice operation. If you made admissions that you were there to purchase sexual services from the undercover their case is fairly strong. If you hire an attorney, and have a clear record, you might be able to get a deal for deferred adjudication where you stay out of trouble and after a certain period of time the charges is dismissed.
If you want to try and keep this off your record, you should hire an attorney.
I cannot reiterate what the previous posters said enough. You need to obtain local counsel who deals with criminal cases in Harris county. Prostitution cases more so than other types of cases will be handled differently by each prosecutor (their personal moral beliefs making an input- a simple fact) and the particular court that you are in as well. Do yourelf a favor and talk to an attorney immediately.