Sudden change in baby-poo

[CUNextTuesday]

My 7 week old DS is EBF apart from a bottle of formula as the last feed of the night (around 11.30). It has been this way for the last 4 weeks since we got a semi-routine established and all through this time his poos have been yellow and runny with bits in, virtually every nappy is dirty so he has quite a throughput. He's put on weight nicely and I haven't had any real concerns, other than I think the formula makes him a bit trumpy.

Last night and today his poo has changed to be much more solid (stickier, perhaps - seems to adhere to his bottom more than the yellow stuff) and greenier, and he does seem in discomfort (lots of leg action). Could the two be linked? I haven't changed his feeding regime at all so I'm a bit mystified. If he is colicky, what is best to do about it? He's not screaming with pain, just is waaah waaah and grizzly and unputdownable...

Green poo could be a sign that he is getting too much lactose (the sugar in Breast milk).
This would be caused by feeding often, but getting too much fore-milk and not getting enough hind milk.
Do you make sure that he feeds on one breast enough to get the hind milk as well?

If that's not the cause, it is possible that he might have a bug of some sort.

It is entirely possible. As soon as he starts to faff and do that head-shaking thing I tend to try him with the other. So perhaps that's it. Don't think he's ill, he's v energetic...