Hello!  I'm Eleonora and I'm 20.

My last period was on 25th of May and ended on 30th. My cycle variates around 21 to 28 days (the latest I ever had,  when I was stressed with my exams). Now it's late for 13 days and I only have mild cramps. I had unprotected sex several times, but always used the pull out method.  For the past weeks I also started exercising heavier than I did before (I would go running in the morning on an empty stomach for 30 to 50 minutes and do some more HIIT exercises in the evening for either 20 or 30 minutes,  followed by some more minutes of toning exercises (so in total it was around 30 to one hour exercises). I would also eat for the past month around 1200 calories,  but in some days when I was stressed probably more,   since it was the time of my exams and was very stressed over that. I am also underweight: 50.2 kg now and 1.74 meters height. I've lost  around 4 kilos this month. Took two pregnancy  test,  one when my period was 8 days late- it was negative the WHOLE day and then the second day another faint line appeared and another one this morning-it is also negative (both have been taken in the morning).  

Also,  for the past month I also slept less than 7 hours per night because of my exams. 

So my question is: might I be pregnant,  or might my period be late because of exhausting my body lately?