You need to talk to the father of the baby and then discuss your options. If you don't want to raise a child then he might and if he doesn't then there are countless couples who are desperate to adopt a baby.
You mean YOUR baby. Not THE baby!
Have a healthy pregnancy. Deliver your healthy baby. Give your baby up for adoption. Then get your tubes tied!
Talk to your doctor about it; he might have a solution.
Talk to your baby's daddy.