Two cavities + confused

So I have pretty bad dental anxiety that led to me not going to the dentist for over a year. I eventually went three months ago, got x-rays done, cleaning, ect, and they told me there were no issues.

But today, I was flossing, and noticed a small hole in two of my molars that I can only assume are cavities. I'm pretty upset and anxious about it, because I've never had a cavity in my adult teeth before, and like I said, dental anxiety.

But I'm also confused, because I feel like 3 months isn't that long of a time. Can multiple visible cavities really form that quickly, or is it possible for my dentist to have missed them even with x-rays? I'm really stressed about it, and struggling to trust them now.