I've put the date you had sex into an online calendar, and basically you're due now. The way is calculated is a bit more complicated than that, but your due date is likely this week. Babies can be a couple of weeks late sometimes, but you could go into labour at any time, so please do talk to someone about this tomorrow.
You are brave and strong and you can do this. 14 is young, but your body will probably cope with labour better than someone who is a lot older. But please don't try to do it by yourself. Having a baby with doctors and midwives looking after you is very, very safe, but without their expert care, it can be very dangerous.
I'd urge you to talk to your mum. Whether that's now, or when you go into labour, or afterwards, she will find out, as you'll have a baby with you!
And as terrifying as that is, its a good thing that your mum will find out, because you'll need her love and support. I hope you manage to tell her before the baby comes so she can be with you and hold your hand.
She may be upset at first (possibly seem angry) but that'll mostly be the shock, though she probably guesses that something is up already. Once that passes, it'll be done, and she can start supporting you, and you can plan for the future together. You'll feel a huge sense of relief once she knows.
It might be easier if you write a letter to her and then maybe go and stay round your friends for a night or so, so that you don't have to have the conversation face to face with her.
Right, practicalities wise...
You'll need to pack a bag with stuff in it for you and the baby. For you, as a minimum, you'll need some pj's /nightie and a pack of maternity pads (you'll have a very long, very heavy period after birth--nothing too worry about, but you'll need something a bit thicker than your Always pads. Also pack some big pants. Like the ones you're granny probably wears,. Don't pack anything fancy or thongs or anything like that. Pack your toothbrush, some washing stuff and comfy clothes to come home in.
For baby, as, a minimum you'll need a pack of newborn vests and babygrows (a pack from primark will do fine) a cheap blanket (if you can't afford that, pack a towel), hat, nappies and some wipes or cotton wool.
Most people for hospital will pack extra stuff like extra clothes, a big towel for you (not white), phone charger, sweets etc, if you've got time, pack whatever you want. Make sure you've got loads of space free on your phone as you'll want to take loads of pictures.
Have a think about whether you want to bottle feed, breast feed or do a mixture. Totally up to you, and you can probably decide when the time comes, but it's good to have a think.
You'll also need a plan for where you are going to live with your baby - are you wanting to go back home? Your mum will hopefully be able to help you claim any money you are entitled to, like child benefits.
It's much better to have a baby with support. I'm married and more than twice your age, but I need support in pregw, and wouldn't want to go through birth alone. You've got nothing to be ashamed of, and deserve to have someobe at your side to help you. Not because you're young, but because we all need that support.