Thanks for the replies. Dr's appt in a few hours, hopefully I can get somewhere with him!

My friend's DS had toddler diarreah(sp) which (I think) was food was travelling through his gut too quickly to be absorbed, he was FTT and once diagnosed they increased the amount of fat in his diet (chips, cakes) and he started growing & getting formed poos.
Both my boys were labelled FTT Brendan around 4 months and Tristan at around 8 months, so they've been on a higher fat and protein diet since then. We don't give them too much of the 'bad' fats (chips, ect) but they do get creamy things, extra formula added to their drinks, ect.