How much did you pay for it? From your description it sounds like a male to me. Are you rolling your thumb toward the cloaca, or are you trying to push it by sliding? I always found that rolling your thumb works very well. From what I have seen, some of the larger males can be harder to pop than babies are, so its not as reliable, but if you try a few times you may get it... Also, I'm not a pro like some of these other guys are, so wait until they comment to take my advice seriously