Why wont my rear wiper fluid work on my 2004 Pontiac Vibe?

[Keith]

So i got a new car 2004 Pontiac Vibe manual transmission ( yay i guess lol not as easy to drive as i thought) I accidently used my rear wiper fluids and i was excited i discovered a new lil button lol but now when i want to make that happen again... it doesnt. I looked at the manual and it says to move the knob on it all the up or down and ive done that but it just makes the wipers move and it just sprays it on the front and not the back. Could i just be low on wiper fluid or is it a mechanical thing? Any tips or settings or tricks or w/e will be of great help, im still playing with it trying to figure it out but it gettings frustrating