If the regex is really just a sequence of dots followed by a question mark, asterisk or nothing, thus cannot contain literals, the only thing you need to check for is the length of the string.

The minimum length will be the number of dots without a quantifier (i.e. exactly one character). If there is any dot followed by an asterisk, there is no maximum length. Otherwise, the maximum length will be the minimum length plus the number of dots followed by a question mark.

Writing the code for this is left as an exercise to the reader. ;)