"Ain't" is fairly regional in the US, and also kind of a class indicator. Class is not quite right but it's close. In general you find it used a lot more frequently in the south, and also generally in lower income populations. It's also less common among folks for whom English is their 2nd (+) language.

If you like it, keep using it! Language should feel good.

Edit: missed your "please tell me" part - it does stick out a bit the way you use it. It's a very casual and informal word, almost to the point of being crass, and it doesn't normally get used in the kinds of eloquent writing you do.