Any advice would be great!!!

So I’ve never had perfectly regular periods - they’ve always been slightly irregular - but recently they’ve just gone crazy. I had a period in June - but then missed July. I thought it could just be down to stress. If I would have had a period, I would have come on whilst I was on holiday - so I got the 3 a day tablets from the doctor that postpone the period and you come on 3 days after you stop taking it... I did and it was a normal period. That was August and I’ve not had another period since.... has anyone any ideas? I’m 17 and have been having periods for 6/7 years now so they have settled into somewhat of a routine. I’m going to the doctors to get it sorted, there’s also a chance I could have PCOS🤷🏻‍♀️ any advice would be great