We've had this problem with DS (now 14 months) ever since he started solids. He has continued to breastfeed with gusto but was still going for days without a poo and then grunting and straining (and occasionally crying)to produce little, rock-hard poos. I've mostly managed to keep him fairly regular by avoiding bananas, potato, white flour and giving too much meat. He has large quantities of fruit in his diet and has a pear for breakfast almost every day. When it's gotten particularly bad I've added stewed prunes to his porridge, encouraged extra fluid intake by giving him extremely dilute apple juice, and once he's ended up needing coloxyl for about a week until things got moving again.

I find I really need to stay on top of things - if my Mum gives him a banana at the wrong time, it can affect him for a week as he gets blocked up and it takes more of those other foods to clear. Hope this is just a short term thing for your little guy. Who would have thought we'd get so invested in someone elses poo, eh?!!!