Could I have adddison's disease if online disease tracker says so? I am 18

Not likely. It's not very likely, as addison's disease is rare (about 40-60 cases per 1 million people) and usually presents between ages 30-50. President kennedy was one such person. It would be best to see your primary care physician about your concerns -- that way you can have a conversation and a thorough evaluation, rather than guessing (which can be scary for anybody). Good luck to you.