Sorry you feel so rotten and who could blame you, but.... time for a bit of tough love now (!).... it won't get better unless you take charge. Easy said i know but you have to shake yourself take a deepo breath and one thing at a time start to regain control.
Not taking 4 yr old to nursery may feel easier than having to leave house, but he's one more person for you to have to think about etc while he's in the house. Is there anyone that could do you a favour and take him for a week while you start to get things sorted.
Colic - yeah that is rubbish, but won't go on for ever and just do what you can while it lasts. infacol before feeds, colief.... I don't really know as I was very lucky and escaped this. Maybe if carring baby around helps get a sling thing and just have him/her wrapped round you while you do stuff in the house.
Go and put a wash on now - just do it. it'll take 5 minures and you'll feel so much better.
Who cares about not being dresses! Don't worry about it.
Don't be too hard on yourself babes and just do a bit at a time and it will get better. Maybe you have Post natal depression??? There are loads of threads where that has been discussed and maybe you should see your GP about it. Don't underestimate PND.
You're so young and with 3 young kids and and all that goes with it you must be a bit down and really shattered. Ask for help and just try and tackly the small things and the big stuff will follow.
You're going to be fine, you just need help for a bit, we all do sometimes.
Keep posing.
Lots of love, and sympathy , xx