Detecting plugins

So I found that

is_plugin_active()

does what I want it to – how ever there is a small hitch. I wrote a method that states:

if on the plugins page and the plugin is active with the active message – display a message for that plugin.

all works fine, the problem is: How do I say – if plugin is ALREADY active do nothing, else if plugin has JUST been activated then do something.

This is all inside of a theme.