baby poo question!

[SpecialCircumstances]

Hi
Just wondering if anyone can help- my DS is 7 months old and has been eating solids for the last month or so, we do baby led weaning so he eats 'chunks' of stuff, sometimes loads, sometimes just a bit.
Anyway he's always gone a but red when pooing, but now goes bright red and looks like he's really straining to poo, today he even cried out a little bit. When he goes it's not hard, just fairly umm 'well formed'
He probably goes once a day, but not huge amounts, and then every few days he does a big one!
I was wondering if maybe he's not drinking enough? As he's upped his solids he's started to take less breast milk, but probably has a 6/7 feeds a day, lots of fresh veg/fruit, cheese, not too much bread.
Any advice?

Could be lack of fluids... Do you give him a beaker or doidy cup of water at meals? Is he having too much wheat- cereals, pasta, bread etc?
On flip side I remember it being a bit of a shock even noticing DS was trying to poo at the weaning stage. Up to then the poo just.. Arrived!!