It doesn't matter what I think your chances are. You're beyond that. You need to know for certain. You've waited entirely too long already to find out whether you are or not.
You need to sit your mother down. You need to MAKE her listen to you. Do you understand that you need medical attention if you're almost 6 months pregnant? Your baby deserves prenatal care. And at 14 years old, your body isn't 100% ready to give birth. Your pregnancy might be classified as high risk. You need ultrasounds to precisely date the pregnancy, and you need to be closely monitored by a doctor or midwife.
Your parents need to know. Keeping this a secret isn't an option. Either they threaten to kick you out now, or you wait until you give birth to a baby who might be sick because you never got treatment and they kick you and your BABY out later. Your parents might not even kick you out. They probably won't be thrilled, but they probably WILL help you.
If you're pregnant, you're going to be somebody's mother. Be a strong mother for your baby and do the right thing. Take a deep breath and tell your parents. Get proper medical care. You need to be brave and do this. You're not a little kid who has the luxury of being scared anymore. You need to step up and become the mother your baby needs you to be.
Tell your parents. Get tested. And if you're not pregnant, have your mother get you on birth control.