Yes, seems like a growth spurt to me too. When I started solids with my lo, she was 5 months old, and I'd say we pretty quickly progressed to 3 meals a day, so by 5 1/2 months she was eating three times a day, with 6 bottles of 4 oz each in the entire day. So, try giving her more calories during the day and see if that helps.
Good luck!