I had to get the traditional medicaid through my local Jobs and family services and no place around here would accept it either, but after a month of having it, I got to choose between 2 different types of "better" medicaid (where I live it's Molina and CareSource, but I have no idea what they offer in Texas). Maybe you can look into and see if they offer a different insurance company through the medicaid.
You should have received a provider list with your medicaid when you were approved :-(. Perhaps they have an online provider list?
Call your insurance and they should give you a list of gyns.
I don't live in Texas, but have you tried googling? Or even getting on the Medicaid website to find a ob?