Periods are late for all kinds of reasons, particularly in young women.
If you are having unprotected sex at 17, do you have a back-up plan? What did you and your boyfriend/boyfriends discuss when you became sexually active? If you are using some kind of protection, do you know how effective it is and what the failure rate is?
Here's one thing to consider: if you are pregnant you have a problem. (More on this later.) If you are not pregnant, you can get pregnant now while you fool around with tests. So stop having sex until you get this sorted out.
Home tests are not always accurate, especially in the early stages. Stop spending money on them for now.
Do you have a doctor? Go and get a blood test. If you want to go to a local clinic or Planned Parenthood, call and ask them to work with you re a payment plan.
I'm not sure why you think you can't go to your mom with your concerns and can only go when you are pregnant. What is the reason for that? Is she in favor of a pregnancy? I doubt that! Are you hoping to spare her the knowledge of your sexual activity unless you have no choice? If you were pregnant, what would you do? Why can't you say that your period is more than a week late, and you know there might be a variety of reasons for that, and can you see the doctor?
I suggest you talk to your mother about your dilemma and get her involved in helping you through this, or helping you prevent it going forward. If you absolutely cannot talk to her, find someone else - a school nurse, a Planned Parenthood counselor, an older friend or relative, someone whose judgment you trust. DO NOT talk to your friends about this - they don't know anymore than you do.
Look, you're 7 days late. In the old days before home pregnancy tests, women waited for weeks and weeks to be able to get an accurate test. Talk to the pharmacist about an alternative test that might be more reliable than the brand you chose. Maybe you used a cheap one from the dollar store and it's either inaccurate or expired. Or, maybe you're not pregnant.
But you really have to stop having sex until you are prepared for every possible outcome of every sexual act. That means pregnancy, sexually transmitted infections, and the emotional upheaval you are experiencing now.