Dilly Dally.
I think that the best thing to do is to wear make up and practice at home!
It may sound a bit silly but taking pictures of yourself or having your friends take pictures of you will really help you find which angle suits you best!
Researching poses and practicing your character's signature smile, pose or whatsoever whenever you have the time would work too!
Another reason why you might seem un-photogenic might be because of the lighting.
Convention lighting isn't that good and chances are pictures taken with a flash makes you look a little haggard.
Best of luck! 3nodding Shilly shally.