Are you breastfeeding or bottle feeding? I'm not able to give much advice if the bottle is the way, but if you breastfeeding, perhaps its something in your diet? The main triggers are caffiene, chocolate, onions and there are a few other things that could be an issue, but perhaps there is just an intolerance to something you have eaten?
We had major problems with my daughter with colic and tummy pains, and it took me a while to figure out that chocolate and caffiene were completely out for me.
We used to do babymassage every day/night before bed, and would massage the tummy in an anti-clockwise direction (I think??) as this is the way the bowel works. We would often had to hold up her legs and pull them apart to help wiht a poo.

Ignore your MIL and maybe talk to your MCHN for a bit of help. SOme of them are useless, but you might be lucky and have a good one!

Sorry I'm not much more help - we spent hours of everyday rocking Jenna on our chest coping wiht all the pains and spew, so its all a little hazy to me now!