This is normal behaviour.
U need not give formula feeds if your production is ok.
The cluster feeding behaviour is sometimes exhibited by many children… children Gulp milk much more than needed , and then prepare for hibernation … that is for long sleep, to complete the sleep cycles.
It could also be due to hind milk not being given.
When you feed from one breast, make sure u feed for at least 20-25 mins (time counted of only active suckling and not intervals and breaks) so that baby gets hind milk as well, which will put the baby to sleep.
Next Steps
Consult in person for detailed discussion