A man is turned into a woman and is compelled to have sex with a male thing that's hunting her

So I'm trying to remember what the name of this movie was so I can watch it. All I remember is it involves a man that gets experimented on and is then turned into a woman when near some sort of creature. But he returns to a man when not near it. And said creature also has some kind of affect on her to make her want to have sex with it. And then one day he manages to escape captivity with the help of a comrade that manages to find him but then the creature gets lose too and starts hunting them down so it can do the thing with her. Any help on figuring out what this movie is would be greatly appreciated.