If you attend meetings then it is likely that you will be having existential anxieties fanned to great peaks so that the comfort and safety of being one of Jehovahs witnesses can then be stressed. This is played out over and over again in the meetings. Since you do not believe anymore all you are left with is the anxiety. And if you have emotional highs and lows anyway (normal as you 16) you are in for a very rough time.
You have been given lots of good advice about seeing your family doctor. Meanwhile try to focus on the things that you like doing. do you exercise, run, play football or go to the gym? what about your school? do you like studying?