I want to do this.So why I feel so sad now?

I'm 39 I had a 24yrs old daughter and 14yrs old son and 2 granddaughters. I had 5 sisters and one of them can't have any kids since I already have my kids I told my sister I'll have one for her and I did I had the baby 5 days ago I was fine and happy with helping my sister to become a mother but now that I saw the baby I'm a wrack I can't help it cry no stop I want her to be a mother and I'm single with a little income I know the baby will be better with her she is married and was so ready to be a mom PLEASE help me to get feeling better I really did this so my sister have a chance to be a mother she has been married for 16 years is Christian and have a nice home since I was 5months pregnant she got the baby's room ready and she quit her job to be a 24/7 mom I'm happy for them I just need help myself to feel as the same I think I don't want to feel this way I need to be strong for my 14 yrs old son that lives with me THANKS everybody for your anwsers