Confused.

Hi so the last time i had my period was from August 24-29 i always have about a week period cycles. For the whole month of September I have not gotten it. I have an app in which I always put my periods dates and etc and it has been pretty accurate until now that a whole month of September past and not it says im 8 days late. So basically i feel like its more since i should’ve gotten it around the 20’s of September. I did a pregnancy test last week on a Wednesday and got a negative and then i did one again on sunday and got another negative. I just want to know is it that im pregnant and i still dont have HCG levels high enough to get a positive? Or is my period just extremely late? Since last week i’ve been getting horrible cramps but nothing seems to come down. And my body is usually not like that. I would cramp for probably 2-3 days and then get my period. But this is gone too long. I dont know what it is. I need opinions guys please. I already set an appointment for my GYN this Friday to see what it is.