Money how old is your son? When I first joined this thread I was aiming to feed dd and I for about £20 a week, it was doable but tough. If your ds is at school can he get free school meals? Also could you get food bank vouchers?
Fruit wise, look out for offers and veg is generally quite cheap well broccoli and carrots are anyway.
Have you looked out for anything you can sell? Also keep an eye out on fb buy and sell pages for kids clothes etc.
Being at rock bottom means the only way is up 
Have had another nice but quiet day, dd seems all better really - kids are amazing really. Plan tomos is drs for me and dd and vets for boy cat!