URGENT! Musk turtle sick!

Since yesterday my musk turtle has had trouble opening one of his eyes. It's puffed up and up close looks like he may have scratched it? Maybe this is causing him stress? He does often try to 'itch' his face with his foot/paw. He has been a lot less active today than he usually would be and has been sitting at the bottom of the tank with his eyes closed. He has also been opening his mouth both in and out of the tank. His legs appear to be a little swollen to but that could just be my imagination. He is feeding normally but not responding to our presence in his usual eagerness.