What am I? Exotic turtle bought in Bangkok

Does anyone know what this guy is? I bought him in the local market, and later read that many of these are endangered. In any case, he is growing like a weed, going from about 1 inch on purchase to about 5 inches long now, with an amazingly long neck, at least as long as his body. And with a voracious appetite, we wonder if we are feeding him enough - he is hungry constantly, climbing the walls, and we just keep putting more pellets in his tank - and he gets bigger and bigger. Also, what other than turtle food pellets should we be giving him?

Thanks for any views. Tom