R.J.
You're gonna hate this:
Soooooooooooooooooooooo (deep breath) ooooooooo many possible reasons:
- Stress
- Dieting to lose weight
- Diet in general (including certain things like soy, to missing certain things like iron... but any of 100+ possible things in one's diet can put an oar in)
- Exercise
- Alpha females (if you're around any other females, your period can 'reset' to match theirs. If you're around them intermittently, it can go back and forth. Where it can get really wacky is when you're around girls going through puberty with a ton of start/stopping. But any alpha female pheramone set can run amok with everyone else's cycles. When 2 alphas get together, it gets even quirkier)
- Illness (like catching a cold / flu/ heck... even a yeast infection or athletes foot... anything that kicks your immune system into gear)
- Endometriosis
- Cysts
- Hormones
- Perimenopause
...................................... and the list just goes on.
It's why... if it starts happening a lot... doctors run bloodwork and do a history up. They run about 70 exclusionary tests -pretty cool off of 1-3 vials of blood, and a cup of urine) which look for the big bads (like hormone levels), along with things like sugar in your urine, proteins, well. Like I said. About 70 things get xd off with blood and urine. About another 50 off of the oral history. So, maybe 130 things get crossed off with the one "This is weird" visit. Or a few things get highlighted as MAYBEs... and more tests. IF it's not immediately obvious (like you started a diet, or lost a loved one recently).