I would say if you did speak on time, then it is AS. If you don't "forget" how to speak, but just do not do it, you still have not lost the ability to speak, you just choose not to--no matter how subconcious this decision might feel. That is not a good explanation. There are people with autism who are CAPABLE of speaking words, but do not. Then there are those who are incapable of speaking words. You are obviously capable because you do not. If it is a regression, you would have to be retaught how to speak. If that is not the case, then it is not a regression, but just a choice of not using words (I don't like the word choice here, but I can't think of a more appropriate one--I have no idea what the scientific explanation or terminology is for autistic people who can talk but sometimes don't).
When you were a baby and you spoke on time, I would say that would be AS. When did you start talking? I qualify for a diagnosis of classic autism--going to get reevaluated in a couple weeks. I did not speak until after the age of 2 1/2, then a few months later at the age of 3, I regressed entirely and could not speak a single word. It was not selective mutism or anything related to selective mutism under a different label because I had to be retaught very slowly how to speak again from scratch. If that is similar to your experience, I would say you have classic autism. If you were on time, and you have selective mutism (or anything related to selective mutism under a different label), I would say AS would be more accurate...or even PDDNOS.