Jackie,
Firstly, I understand your stress. Leave any child crying anyway is really stressfull, when I leave for work, if my two girls don't say goodbye, I can't leave the house.
From my experience with my 2 children, the foundation for happy children (most ages) is routine. If you do the same thing, evey single day, 7 days a week, your child knowns where they stand. There are no surprises, no changes, they know what to expect, and feel secure. You son is telling you he is unhappy and insecure.
In your case your child is 11 months, at 11 months, memory isn't far developed, having 2 day in nursery, two days out , one back in, and then two out, is confusing. I would suggest keeping the three days in, then four out. He will identify with this quicker.
He will also indentify with the current regime, however this may take some time, if he does to some degree.
Keeping you child at home is nonsense. Allowing your child to meet new people and children will only give your child confidence.