S.H.
I, feel you should up his Formula quantity.
AND, yes, it could definitely be a growth-spurt... that he is still trying to get enough intake for & catch up with, since typically growth-spurts occur at about 6 months old. And he is past 6 months old already.
According to my children's Pediatrician... for the 1st year of life, Breastmilk/Formula is the PRIMARY source of nutrition for a baby... NOT solids, and NOT other liquids, and to still feed on demand 24/7.
My kids, at that age, drank more than 6 oz. bottles of breast or Formula, and more frequently even though they were totally on solids by that point, and my kids had GINORMOUS appetites... throughout the day, and they grew like weeds.
I think, your son is simply needing more intake... Formula wise. It has more nutrients ( a wider spectrum of it plus iron) in it, than say a bottle of baby food even if given 3 times a day.
A great book is "What TO Expect The First Year" and it can be found at any bookstore or online.
For me, I would first as a matter of deduction, increase his bottle/Formula quantity... instead of giving him just 6 oz. Try putting more in the bottle... and if he drinks ALL of it with no problem... then he probably needs more.
Another growth-spurt will occur at 9 months old... then 12 months old...then 15 months old and so forth.
I think your baby boy is growing a lot right now, since 6 months old, and he will probably be hitting some milestones soon, and other developmental changes. Often, a change in appetite and sleep is a forewarning of these changes coming up, if it has not already occurred.
All the best,
Susan