Oh GS you sound so tired and down :(
I sympathise, sometimes cooking is just tooooo much.
Do you shop online for groceries?
My main advice would be to make sure you've got plenty of healthy salad stuff in the house. At 7 months, babies don't really need 'meals' per se, you can just stick a load of random stuff on the high chair tray and let them get on with it - while you sit down with a ready meal or tinned soup :o
Stuff like avocado is great, so healthy and you just need to chop it up. I am quite strict on salt too; you can get no-added-salt rice cakes (Kallo iirc?) then just cucumber, carrot sticks etc. Cream cheese to dip, or hummus.
If you can afford it, go for ready prepared stuff like grated/sliced cheese, pre cut veggies etc - slight price premium but it's totally worth it while you find your feet.
I agree with the bulk cooking thing - when DH is home looking after the DCs, make a big batch of a few different things, soup, sauce for pasta, stew etc and freeze. Boots do salt free stock cubes. Invest in some decent Tupperware.
HTH - and please don't beat yourself up!