Creative Slump

I've been in this slump for almost 6 months now. No sketching, no new ideas nothing. It's really frustrating to say the least. Not sure what I have to do to come out of this. It use to be anything that would spark my creative juices weather it was a commercial, a bug on the window, a crackhead walking down the street etc. Now it seems those things aren't merely enough to help me anymore. So what will I do? I can't force myself to draw because that will only have me sitting at a blank sketchbook for hours. Which is just a waste of time. I've tried walking around the city, but that doesn't help and it only pisses me off even further (tourists). I guess I'll just keep at it and see how it pans out but I need to get my focus back.