Hi there,
Have you read any information from Dr. Brazelton on child rearing? He is an excellent resource.
http://www.brazelton.org/main.html http://www.babycenter.com/?h=true http://parentcenter.babycenter.com/
Time management is really a tough one - how helpful is your husband? Do you have family close that someone can come in and help you a couple times a week even? To give you a break? Do you do meal planning for a week at a time - using a crock pot eases some of the cooking stress. I realize you have a great many expectations and demands placed on you - but you need to find out how to delegate some of that out to people who can help you. I worry about your own physical health, not to mention being emotionally exhausted.
About your oldest child - you may well have to allow her to have her tantrums and not pick her up each time. Unspoiling a child is alot harder than spoiling one. Allowing a child, even an infant, to cry is not a bad thing. Even removing the child with the tantrum to another room for, in this case, a very short period of time, is not a bad thing either.
Is there a group of moms with preschool children in your community that you can access? Other moms surely have faced similar problems and can give you some solid advice. Maybe even through your church. I do not know your community resources but perhaps you can find out. There are some places that have the Early Head Start Centers that children younger than three can access. Does not mean your daughter HAS to go there all day - but even a couple hours a couple times a week.
I truly wish you all the best. You have more than your hands full and hope you get the physical and moral support you need.