3 and a half month old sleep

[Havingabeer]

He was going from 7pm until anywhere between 2am and 4am. This stopped about a fortnight ago. Now he's waking anywhere from 10pm.

What do I do?

Exclusively breastfed. I've been leaving him a bit to resettle with mixed success

Sounds like the 4 month sleep regression. No advice, you might just have to ride it out. Sleep when you can, etc!