I am dealing with something similar myself. My DS is 13 months old and although he started eating well when we started weaning him, he seems to not have progressed exponentially.
When you say 'milk' do you mean milk or formula?
Below is what I came to think, maybe something will be of help to you
1- He is teething, so that always makes him get off food somewhat.
2- I am giving him formula, which as I understand takes longer to digest. I want him to have all those nutrients, but I decided to up the number of 'milk' bottles and keep the formula for the evening/night, when having a fuller stomach might help his sleep, too.
3- I think it is partly a controlling thing. His world is so big now, and food is the only thing he can control. He can decide (probably against his better judgement) now that potatoes are bleah, carrots are stupid, fish is good, but banana is boring.
He might also be distracted by all the novelty around him, so he decides that playing with a toy is more important than eating.
4- They are still so, so, so little. After all my ds started with food when he was 6-7 months, and he is only double that. Perhaps not all babies need to eat a lot when at this age, perhaps he finds food still very 'new', so a bottle is something much more comforting than having to try or chew food when he cannot be bothered with that. Or perhaps I am expecting him to be more like 'adults' and eat progressively more and as often as we do. Perhaps he also is not at a stage when 3 proper meals a day are the normality in his daily life.
I am not sure whether this is of any help at all, but I read yesterday here on MN that babies do not go hungry if they are hungry, so I decided to take a step back, offer him food, and if he has it great, otherwise I know that he is having milk/formula anyway. Tomorrow is another day and we will see.