Bless you. I'm 36 weeks and I didn't have my implant out until July so you must be about due or even overdue now, and you really do need medical help.
I think anybody you told would just want to help you, can you pop to your walk in centre and speak to somebody there this evening? Do you have sexual health clinics close?
You could make an appointment with your GP in the morning. Any of these people will be able to give you some advice now, and then support you in telling family and help with that if you need.
I think if you say how young you are, nobody here is going to judge you, but we might be able to give more appropriate advice or age appropriate advice maybe.
Is there anybody at school or college you can speak to if you go there?
If it was my daughter, I'd hope that if she was brave enough to post for help here, that she was brave enough to either tell me or somebody else as soon as possible afterwards so that you can have the right medical care in place.
Things like whooping cough vaccination you might have missed but midwives might need to do a blood test and check what blood group you are so they know what to give you should you loose blood giving birth and need more, or need a genera anaesthetic.
Plus you will need lots of support, and as quick as you've talked to somebody and everybody's emotions are out the way, you can make sure you have that before baby arrives.