Also, just FYI that my DD was eating fruit exclusively when we started solids, and that's when her constipation started. Going back to EBF alleviated it. But aside from that, the only thing that has really made a difference for US was limiting fiber intake along with increasing fat and protein.
I don't know if it has been mentioned since this thread started a while ago, but supplementing magnesium and vitamin C has helped a lot of LOs suffering from constipation. Our ped actually sells the mag supplement - Natural Calm - in her office (why she didn't tell me this before Rx lactulose, I have no idea). I didn't have much luck getting DD to take it (although she does love vit C), but I give her epsom salt baths almost daily. I've been told that mag is well-absorbed through the skin so that's why the baths work.
As far as MoM, that worked for a little while with DD, but then stopped working. Plus, I started reading that it's not good to take long term. I do think it's one of the better alternatives as far as internal laxatives go.
Also, have you started using an aloe or lubricating jelly (I get "un-petroleum" jelly) to help make it less painful? That helped DD get over the fear - making it really easy for the poop to slide out.