Cluster feeding at 5 1/2 months?

So my 5 1/2 month old has had sporadic feedings lately, waking up 4-5 times a night when she used to wake up maybe once. She feeds and goes right back to bed. I have started supplementing with formula because I have had supply issues and thought maybe she wasn’t getting a full 5-6 oz of milk while breastfeeding.

Even after formula she’s eating like every 1.5 hours, 3-4 oz at a time. Can they cluster feed this late? I looked up growth spurts and said there’s one normally at 6 months. Maybe it came early? Help!