My periods are really irregular suddenly?

So on the 6th May, I came on my period, nothing abnormal, I was expecting it, but then I came on again on the 29th May, which was a little odd as normally my periods are every 30 days or so, I didn’t think much of it, but now I’ve came on again (20th June) which is the 13 days after my last one ended. I’m really confused and don’t know what’s going on.

I’m 18, still a virgin so not pregnant, I’m not on any contraception or anything, I have been feeling anxious and really emotional lately but I put that down to pms??. I think I’ll go the doctors if it’s significantly early next time.

Anyone else experienced this or can give me some peace at mind???