Hi kiwilaurie
DD was 7 weeks when we put her on a 3 hourly routine due to slow weight gain (and I went on Motilium for my milk supply).
I was told by Plunket and Family Centre to keep her up for 1 hour to 1 hour 15 mins as she was getting overtired.I had to stroke her face etc to encourage her to keep feeding for the full feed.
What happens if you put Jackson to bed after the hour or hour 15 mins? I found this was the only way i could keep to the 3 hour routine. It did take a couple of days to get used to, but then worked out really well.
in saying this, it could be a growth spurt!
I hope you get it sorted soon

and are able to get some rest. Take care