Can I say if i actually have POTS or not?

So I got brushed off for months because I have another chronic illness, but the department called my gp and said it had nothing to do with my other illness so they looked into it, send a letter to cardiology who said yeah we think you have pots and I got send a heart foundation website to help manage pots, but there’s nothing on my actual medical diagnosis and they said they won’t diagnose me unless I really want to because it’s common? My family say that means I can say I have the condition because i can tell my school as it’s been affecting my education terribly, but I feel like I can’t say that i actually have it because they haven’t written it down? And I don’t wanna be a self-diagnosed especially as I’ve seen a lot of people fake POTS on the internet, I hope that part doesn’t sound rude!