I assume PT means "part time"? I think you're someone who's done a degree that's used some maths, and whatever you do now also uses some maths - because of this, you believe it's ok to call yourself a mathematician.
I have a degree in maths, Cert of Advanced Study and am in the middle of a PhD - and I wouldn't call myself a mathematician (I'm currently a PhD candidate). The fact that you seemed to think that learning how to integrate in A-Levels had anything to do with asymptotic analysis reinforces my opinion that you're someone who likes to talk "maths", but isn't all that clued up! Don't get me wrong - I'm sure you know more maths than the average A-Level student, but to call yourself a mathematician is bordering on the ridiculous - I honestly don't think you'd pass a degree-level exam in the subject. Sorry if I'm being harsh, but it's a pet hate of mine.