Just need some advice.

I’m 28 days late on my period. I have a 35 day cycle and for the last 6 months it has been very consistent. I tested for pregnancy for the first time 2 and a half weeks ago and it was negative. Since then I have tested 3 more times and also negative. I’ve heard about women being pregnant and it not showing positive until months later, but if I’m not, does anyone know how to “jump start” a period? I have a good sleeping schedule, I eat mostly healthy and exercise a bit. Idk what else I can do. Thanks in advance.