Have any of you had issues with this thermoter. I've only used it a handful of times and today I went to check LO's temp since she has been congested and coughing AGAIN! anyway I turned it on and the screen lit up and then went off. And now it wont come on at all. I am really dissapointed with this. Am I supposed to change the battery or something? I've only used it a few times though so I'm surprised it would just stop working like that