Hi and thanks for your question. It's understandable that you feel really worried—it's pretty scary thinking that you might be pregnant.

The fact that you had a negative home pregnancy test is good. The tests are quite accurate (about 95%). These tests detect the pregnancy hormone hCG in urine. Sometimes if urine tests they are done too early or if you don't have much hCG in your urine you may get what is called a false negative. This means the test is negative but you are actually pregnant. This is rare but does happen, especially if the test is done under 4 weeks since your last period.

I would say that the chances are that the test is correct and you are not pregnant, but wait another week and if your period hasn't come then repeat the test. If your period still doesn't come after that it would be good idea to see a doctor or nurse and have a blood test for pregnancy. These are 100% accurate.
Being very stressed, as you would be when you are worried you are pregnant, can affect your hormones and may have made your period late. It could also make you moody and tired.

If you have a condom break again you can use emergency contraception if you like. This is a hormone tablet which you take within 72 hours of the sex you are worried about. The sooner you take it after the sex the better. You can get it over the counter in pharmacies but need to be 16 or older to do that. You can also get it from a doctor or nurse.

It's best to always use extra lubricant (water-based) when you are using condoms because it makes them far less likely to break. You might also want to think about using another more reliable type of contraception as well as condoms, so if it happens again you will be protected from pregnancy.

Having a condom break will put you at risk of sexually transmissible infections (STIs) if your partner has had any other partners, so it's important you get tested. A sexual health or family planning clinic is the best place to go if there is one near you, otherwise any doctor you feel comfortable with is fine.

As a last point, I know you've already had sex, but do you know the laws about it? In Victoria it's against the law for anyone to have sex with you if you are younger than 16. Even when you're 16 or 17, it's illegal for someone in a position of care, supervision or authority over you (e.g. teacher, step-parent, sports coach) to have sex with you. If you ever feel forced into something sexual, this is assault and you should tell someone you trust.

All the best and take care.