Help please-Period 65 days late

Ni

I am 16, and I had my last period on the 12 of July to 16th, I started my period at about 11 years, and now I’m 65 days late, took two pregnancy tests with a difference of a month, both came out to be negative, I did gain 8 kg from June, however i think my body would already be used to it, I am trying to loose weight now but it’s hard.... I don’t know what to do, and what it could be.... I have had a period late for 45 days before but never this long! I have headaches and slight back pains in my back about the same time each month, but no blood. And now my ovaries are feeling wierd like I have cramps but they are a bit unusual... I’ve been feeling dizzy last month. I have had Vitamin D problems in March, could that be the reason? Does anyone know what it could be, or did this happened to anyone before?