Does anybody have this brand of BBT? I bought mine last week, the first time I used it I got the 4 beeps when it reached a stable temp but ever since then it hasn't beeped. I can leave it in my mouth for several minutes and it still won't beep however it does seem to reach a temperature after a while and then stop...I don't know if this is my actual temperature and it's just failing to beep or if there is a problem with it?! Help would be much appreciated!