Hi.
The first thing you have to remember now is that your life can only be what you make of it. Though you were the victim of a bad situation as regards your parents, it is really up to you to be a victim of this any further. The only way you can escape a downward spiral that they started is by putting your foot down and making sure you're careful with your life.
Okay, let's talk about the possibilty that you may be pregnant. It is possible that you aren't and that your period is just delayed. I've had a friend who didn't have a period for around three months. She didn't tell me about it because she knew that I'd be worried for her. Your being stressed out may be contributing to it. Most of the pregnancy tests you can buy now are quite reliable and if you've had five all turning out negative, then chances are that you're quite safe.
Now, the more important stuff.
Honey, the only way you can make sure that you don't become a total victim of your parents' lives is by being smarter and ultra careful. That means begging off sex as much as possible. You're not married and sex is not something you just do when there's nothing better on the tube. I'm sorry if I sound harsh but your being on this site must already have shown you how hard some girls have had it since they became parents. A good many of them are really making a good fight in terms of fixing up their lives for the sake of their children but it really would've been simpler if they weren't. It really is easier to study if you're not supposed to breastfeed, clean the baby, help with the burping, etc.
Please beg off sex for now. I'm not even one for safe sex anymore because, as you can see from the other stories here, it isn't really all that safe either.
Spend more time with your mom, both your biolgical mom and your guardian. Try to understand them and see why they are the way they are. I mean, really, your guardian is one hell of a woman for having taken you in. You biological mom is also someone to look up to even in the slightest because she had enough sense to realize that she didn't know how to take care of you.
Though it seems great to have a buddy in a child, it really is better to be more prepared for a baby. Prepared in terms of having a complete family, a mom and a dad who both have finished school and have work and have no qualms (especially for the dad) of giving up nights on the town with buddies. Having children is a wonderful responsibility. CHildren are not pets that are cute. They are human beings that we are gifted with and are responsible for.
Make sure that when you are blessed with a child, you yourself will be a blessing to your child as well.
Please feel free to contact me anytime.
Erick
And you should let your mom know that you might be pregnant. Just incase there's something wrong and you need to go to the doctor. But let me know if you find out anything.... and don't forget that you can talk to me if you need too. 
