How much child support will I be paying if I make around $1800 a month?
For one female child. I live in Louisiana-

Depends on where you live.

What does the other parent make? What are the Childcare costs and insurance? Extraordinary medical expenses? Are there any other kids for either of you? Spousal support? Who does the child live with?

There are many other factors beyond just the one pay. Here is a site that can give you a basic idea

About.com: http://www.alllaw.com/calculators/Childsupport/Louisiana/