This could get a bit gross...if you're eating or weak stomached, be warned!!

My DS2 is 6mths old. He is breastfed and is having 1 or 2 solid meals a day. Mostly only fruit and veggies, though sometimes a little rice or weetbix, and occaisionally some meat is mixed in too (only a tiny bit!).
His poos have always been a little bit of a concern for me. Even when he was fully bf, he was only pooing 1-2 times a week and they were never that big, and were quite... thick. Now they are quite solid and today he has only pooped little bits at a time, and it seems to be a real effort. I know it's usually really unlikely that BF babies get constipated, but I have a feeling pooing is an issue for him. He is feeding 2-3hrly round the clock.
I have a feeling (mummy instincts!) that he has digestive/stomach issues of some sort, though nothing has ever been diagnosed and really, there isn't a big tangible thing I can put my finger on that would make me go 'this is why I think it' itms. Except when he was born he had digestive issues and was refluxing bile for a week after birth. He was in special care and fed (both BM and formula) via NGT for that time. The problem seemed to rectify itself and after a raft of tests, the paed said there seemed to be no problem now.
What should I do? Should I just give him some water maybe? I give him a sippee cup withhis food, but not much water goes in, it's more just for him to get used to water and a cup. Should I give him some formula (though my instinct tells me this will just make him more constipated), I can't really feed him more tahn I do, I feel like I'm feeding him all day as it is!
TIA