Hi there and welcome to BW forums
Although this is your third LO they are all different and whilst one might not take a lot of milk another could be a milk lover.
Your LO is still really tiny, guidance is to start solids at just a couple of teaspoons at 6 months so really for your LO to be eating a third of a weetabix this is a huge amount in baby terms. His dinner sounds big too even if you aren't really sure how much he is digesting he is trying a variety of veg fruit and carbs. It looks to me like the only thing can could really be altered is your expectations of what he 'should' be having. Don't forget his primary food until 12 months is milk and the weaning process is not aiming to drop milk feeds but rather to introduce different tastes and textures and allow LO to make a gradual transition to larger solids meals and eventually a reduction in milk. That reduction in milk is not expected to happen for quite some time yet though.
The DF is usually the first milk feed to be dropped but not until solids are well established and LO could be closer to say 8 months rather than 6 months.
when guidelines say it should be around 20oz mark
These guides are to ensure milk is not reduced too much or too rapidly. If your LO needs milk then he needs milk. Some take a lot more than 'average' milk and some a lot less, LO can usually guide you on the milk intake and at this age he should be taking as much as he needs without being limited.
You can make sure he gets a drink of water with/after solids meals so that he is not thirsty which could possibly lead to greater milk intake but otherwise I wouldn't worry about him having the milk.
When would you recommend I start Lunch?
The general guidance is that a third meal is introduced at around 8 months old. of course some LOs love solids so much they will cry out for food if they see any and a third meal might be introduced earlier than this, with baby leading the way. For others who are not so interested in solids they might not take much at all until say 9 months when their interest picks up but even then it might not be what you'd call a full 'meal'.
he is not keen on the spoon either,
I wouldn't worry about this. Lots of LOs don't like to be spoon fed, they want to self feed. Mine was never spoon fed but I did introduce a small fork quite early on, I would preload it and hold it up for easy grabbing and he would get it to his mouth. Otherwise fingers are fine, there's plenty of time to learn how to use cutlery.
I have literally 15 mins before he starts screaming.
Again I wouldn't worry about this. 15 mins sounds like a reasonable time to sit for food. LOs only really have the patience to sit longer if they want to eat more but will still fuss to get down when they are finished. i'd just offer a couple of bits of food and let him have his 15 mins then meal time is over. There really is no hurry to increase solids.
Hope that's helped to put your mind at ease - lots of us worry about food issues at one point or another so you're not alone there!
