I've struggled with this issue pretty much the entire time I've been nursing. I'm hungry as crap after I pump or nurse. I try to eat often though to stop any lightheadedness. Even so, it seems like a constant struggle. It got a lot better after I stopped eating oatmeal in the mornings. I still take fenugreek (just one pill a day) but now I think that might be making it worse based on this web page. I have stopped taking it a few days here and there but I still get hungry/ lightheaded a lot on those days as well. Also, I'm 20lbs above my pre-pg weight, so I know its not that I don't have enough "in storage" that my body could draw from.
Also, I try to eat a lot of high fiber, high protein foods to stay fuller longer which do seem to help but not as much as you'd think.