I think I've thought of everything, but in my sleep deprived state it's possible I've overlooked something obvious.
He is warm enough.
...but not too warm.
He has plenty of solids during the day.
He is clean.
...and dry.
He has wound down as every evening.
He has had a biiiiig breastfeed before sleep.
There are no particular disturbances overnight.
He is teething a bit and I've given him Calpol accordingly.
Why won't he sleep?
On a good night he wakes up every 2 hours for a feed, plus one extra feed, plus usually spends an hour awake at some point.
(So a typical night would mean feed at 8.00, 10.00, 12.00, 1.00, 2.00, 4.00 awake until 5.00 at which point my 2-year-old gets up and the baby will doze a bit, get up for breakfast and then have an hour's nap before 9.00).
On Friday night he woke 9 times. NINE!
What am I missing?
He's 6 months.