You cannot trigger your own On TEXT events in your own client. When you send a message to a channel or user, there is no acknowledgement from the server sent back to your client to tell you that you spoke in the channel or to a user. mIRC only triggers On TEXT events when a server tells mIRC that somebody spoke.
This is by design, as well, to prevent a script from trigging itself. You will need to create a command /alias to activate your scripted behaviors, or you will need to run a second instance of mIRC to behave as a third-party bot entity.