I'm 16 and i'm sexually active i haven't got my period in about 4 months and i am terrified i might be pregnant took five test and they were negative ?

Pregnancy unlikely: Pregnancy tests are pretty reliable so you need to go with that. At your age irregular cycles are relatively common for a variety of reasons. Meanwhile, if you wish to remain sexually active and you don't want to get pregnant then you at least need to use condoms ALL of the time, and preferably should talk to your doctor about more adequate birth control.

Sexually active: If you are sexually active at 16, you should be responsible for your safety. You should have spoken with your doctor, obtained information at least about contraception. In addition, you should always be using condoms. 5 negative tests are just that, negative tests and so the likelihood of pregnancy is very low. I encourage you to speak to your parent or responsible adult, see your provider.