Feeling lost after having the younger one

Hi, I’m mummy of 3 kids.Elder one is 12 years old, 2nd one is 9 years old and younger one is 5 mths old. I’m fully bf my lo now. After my lo came, my life suddenly changed a lot. I’m felt so stresss to look after my kids, I have to worry my elder n 2nd’s homework, have to do housework, have to cook, have to pump for my lo, have to look after my lo. I felt lost and I don’t have much time to rest. Since delivered, everyday I’m only sleep no more than 5 hours. No Matters how I clean n done the housework, my elder n 2nd one will mess the house and everyday I have to redo n redo. No one is helping me. All I have to do it myself. No matter how I talk to my elder n 2nd one, they just repeat n repeat. I really felt lost. I don’t know how to carry on this kind of lifestyle. :(