You may just need (continuing!) patience. I read various places that lemon trees can take 10 - 15 yrs to start producing and then I found this:
My lemon tree is blooming for the first time this year at 23 years old. Miracle Grow is the only fertilizer I have used. It winters in the house in an unheated room. (05/02/2007)
http://www.thriftyfun.com/tf457596.tip.html
Also it looks like your tree is in the same little pot all these years? Have you repotted at all? Might be getting rootbound by now. Think about going one size up with some fresh soil.