Hello
Some babies thrive on routine, others don't seem to.
I've found with mine the best thing I can do is just try to be consistent.
No matter how much sleep they've had the night before, I get them up at 7:00 and start over.
Jordan's usually ready for another sleep by 9:00, and from then on around every 2 hours, with a micro nap while he's feeding around 4:30 - 5:00, and then down at 7:00 again.
My eldest still wakes around 7:00 on her own, has a nap at midday and is down again at 7:00 at night.
hth