How long have you thought? Time plays a huge part, it could defintiely be exam stress so make sure its been some time that you've noticed. There are definitely things you can do to help you, e.g. brown noise on youtube works really well for ADHD, and spaced repetition is an ADHD proven to work technique. Maybe you should try find things online to help you, and then after exams then you can start a log/diary of behaviours and specific moments you noticed evident ADHD behaviours, and then show that to your parents- you can then really reflect on whether thats been going for a while and match up your behvaviours, and that way you can be sure its not exam stress. Best way is to write a one sentence summary of the most stressful thing that happened on each day, and then symptoms/behaviours, so you can be sure that it doesnt ONLY happen on stressful days, even if its more prominent on stressful days which it most likely will be, so if you develop a log of a lot of symptoms over a long period of time then thats substantial enough to show your parents- but do it after exams because then you'll get stressed seeing the behaviours build up.
p.s. i have brown parents and adhd