Great napper but night wakings every 30 mins?!

My four month old has never slept well at night. He falls asleep easily but does not stay asleep at night for longer than 30 mins (except for first stretch of night which is 1.5-2.5 hours). Occasionally we can pat him and put his pacifier back to get another 30 mins. Often if we try to soothe him in the crib, he gets ore and more upset resulting in full in crying and having to bounce him to sleep again. He is bottle fed and gets three throughout the night when it is obvious he is really hungry. He sleeps in a crib in his nursery and I sleep in a bed beside him. White noise, dark room, consistent bedtime routine etc.

Little dude is a great napper, however. WWs are 1.5/1.75/1.75/1.75/1.5.

We are so tired. We are considering Ferber but peditrican suggested waiting until 6 months. What could be causing such frequent night wakings ?! I would be happy w 2-3 hour stretches at this point !