Read Current Url

Is there a way that I can read the current url.

I have an asp page currently such as default.asp?x=1&y=2&z=3

Now I want to keep the existing parameters and attach another parameter
to it and resend to default.asp

As the original parameters are dynamic, and may or may not be
generated, the only way is to read the current url and to simply add my
new parameter such as h=5 to the url.

I don't know how to read the current url.

I tried Request.ServerVariables("SCRIPT_NAME") but that didn't include
the parameters. i.e. it just returned the default.asp