Honestly, what you're describing sounds pretty familiar to a few of us who've been through this stage! At 8 months, milk is still the main source of nutrition, so it's quite normal for babies to still want milk after solids, the solids are really just complementing, not replacing, the milk yet. One of my mum friends actually had her IFC teacher suggest increasing the milk volume per feed when her baby kept signalling hunger, so it might be worth having a conversation with your IFC to see if they can adjust the timing or quantity a little better. The night waking every 2-3 hours does sound exhausting, and while it can be linked to not getting enough calories during the day, it could also just be a developmental phase at this age, some babies go through a rough patch around 8 months regardless of feeding. Do keep an eye on wet diapers as a rough gauge that he's getting enough overall, and since the night waking is quite frequent and you're concerned about his calorie intake, it's really worth bringing this up with your PD to rule out anything else going on!