When I gave ds#1 solids, I always gave them 20-30mins after a bf until 9mo & then swapped to solids them bf. From my perspective, you may have them too spaced out & be causing snacking. Also 2oz seems a lot for a 5.5mo... I work in metric, but looked at a bottle that has oz on the side... there is no way my ds#1 would have had 1oz at 7months & he was 23lb by then. So I think maybe some of the problems may be stomach ache, especially as he is so young & having solids in the evening, I would move it to middle of the day, after the 11.30 feed.
I notice he is on 4 day time feeds, he would still be needing at least one night time feed & despite books it is not uncommon for babies this age to need an extra night feed if they are bf as they tend to be distracted at the 4-8month mark & day feeds can often be a bit less than they need to be, so be mindful of that too.