19yr old, period 2 weeks late, no symptoms, 6 neg hpt.... st

Hello,
I would really appreciate any help that anyone could give me. I am 19 years old. I was suposed to get my period on the 9th. it is now the 25th (Merry christmas). I have taken 6 hpt ( some first response, some e.p.t) on 6 different days throughout the 2 weeks. The last was on the 19th. they have allcome up negative. I have had no real simpoms of period or pregnancy... but have always been regular. This has happened once before last yearr, but i was only a week late. I usually can predict the day! I have never taken the pill and always wear a condom. this past month, my diet has changed, and i gues stress has been up from exams, but nothing I cant handle. I really dont know what could be going on with my body. can anyone give any insight? Thanks so much!!!

~Looking forr answers

It can be from stress. A pregnancy test would have been accurate by now, so pregnancy could be considered unlikely.

Stress and dietary changes could have caused your cycle to act much differently than it normally has.

Stress can affect this time of the month a lot. This happened to me when I was 16 and stressed, and missed for a month. I had never had se til I was 18, so I know I was not pregnant at 16. I went to the doctor with my mom and they ran some tests. I found out my cycle was changing from 21 to 28 days. It finally came after a month and I went back to having a cycle every 28 days, after It skipped a month. The doctor I went to has three daughters, so he should know. Your cycle might be changing too.