Sooner or later you are going to have to tell your parents, because there are doctors appointments you are going to have to go to you should be taking a prenatal vitamin and really how are you going to raise this baby on your own at 18?
You just said your mom thinks she's pregnant..so on top of her having to raise another child of her's, she would pretty much be raising yours financially as well, because let's face it, at 18 there is no way you have a steady job/career, a TON of savings, and more.
It takes on average about $120,000 to raise a child successfully, and i dont think you have that sort of money..
so my question to you, is how are YOU going to raise this child since your boyfriend-if your even still going out with him- does not want to be in the picture.
Being pregnant young is hard enough..doing it alone without spousal support is even harder..and what about school? are you going to finish high school and go to college or university?
Do you live on your own? or still with your parents?
Do you drive yet? do you pay car insurance?
How are you going to pay for YOUR child's health insurance?
There are alot of things to think about here, not only for yourself, but for this baby and your family.
Because they are the one's -your parents- who are going to be affected by this financially, if your mom is indeed pregnant..thats another mouth to feed..
My best advice to you, is look into adoption.
These days, you can have an Open Adoption, which means, you get to be involved in the child's life, recieve updates on how the child is progressing, you could visit the child, recieve photos; some people who do open adoptions even get to go on family holidays too.
I think that would be a really great thing, because not only are you giving the best to that child, you are helping a loving caring family, and you are also able to live out your teen years, finish high school, go on to college start a career and more. And i think that right there is owning up to responsibilities, because without the things i listed above, you really wouldn't be owning up to responsibilities if you just live with your parents, have a small part time job, a bit of savings...that means your parents would be the main care providers of that baby..not you.
So i really think adoption would be wonderful.
And i don't say any of this to be rude.
As to how you should tell your parents, tell them soon, listen to their reaction and response to what you tell them, dont talk back to them, have an open ear, they have a right to get upset, and explain how you are going to take the next step with this now, because that will be a question: "what are you going to do and how are you going to do it"
good luck
if you need to talk PM me any time.