@jespah,
I second that - you are only 16 there is no reason for you to be so stressed out for a job at that age. Your focus should be school and your studies and then the job should be extra. I would suggest you go search out other employment.
It seems you have some good qualities like wanting to get your work done perfectly. Your weakness seems to be speedy. You should look for a job that would be best for your strengths. Hard work, the requires high quality rather than quick service type of work.
It wouldn't hurt to speak with your doctor - but I would shy away from taking medications. Not all jobs require you to be in such stressful quick service.
I have a 16 year old daughter -- I wouldn't want her to work where it would stress her out -- school is stressful enough. She works keeping score for basketball games for youths and umpiring softball games for young girls - not at all stressful. Her work is extra and school and her sports committments come first.