Hugs Fizz.
Yes, stay off with your boy tomorrow, take him back to the doc and be stubborn awkward insistent. And stay off with him next week if you have to. Don't feel guilty about work, they're grown ups, not sick toddlers. They should be able to see that too!
With drops, I read on here to get them to lie on their back with eyes closed. Put a drop in the inside corner of the eye and then when they open their eyes the drop goes in. Helped by weird & wonderful creatures momentarily appearing in the garden ("LOOK! Is that a unicorn?! Oh no, it's gone") it works for F.
Weetabix and custard is probably fairly ok nutritionally. Protein in the custard (and fat, sugar and calcium etc) and weetabix is good carbohydrate and usually fortified with some vitamins. Don't worry about nutrition for a little while yet. If that's what he'll eat, let him eat it.
and more hugs.