Ladies, I need advice (Guys, you may want to stay out)

I'm not a doctor, but first thing that came to mind is to ask if your body fat is too low? Is there a chance that you are underweight at all?

Are you having any other symptoms? Tired, always cold, losing hair, or anything else that is abnormal. For your height, 96lbs isn't bad, but I would be careful. It may be low enough to cause some problems. I had a similar experience, but it was before I really started training, and found out it was due to my thyroid being too low. A lot of other things can cause these types of problems, but the first ones that come to mind is weight (low, high, or rapid change), intense exercise (this one's debatable), and hypothyroid. I hope you can figure out what's going on. I know it can be frustrating.

You might look into getting your thryoid checked, then. The tiredness may be due to how much you're exercising, but it can also be due to hypothyroidism, especially with the menstrual irregularities. That's pretty much how mine started with the intolerance to cold added in along the way. Let me know if you have any more questions.

I'd go to the doctor. Whatever it is, doesn't sound good.

I knew I should have stayed out..

Anyway, I am a doctor and have just finished 9 months of gynaecology (no jokes please). The most likely cause is just the exercise and stress changing the release of hormones and therefore your periods. However, irregular bleeding in the older women (reproductively this is 40+, depressing eh!) should always be investigated by seeing the doctor. Firsly you will need an up to date smear and swabs as well. 'natural' infections can sometimes materialise by irregular bleeding.

Bottom line is if you are near or over 40 see a doctor tomorrow. Under 40, get a smear etc then see how it goes. For peace of mind a gynaecologist appt might be a good idea.

I'll throw in another vote for having your thyroid checked.  I had similar issues, missed periods, severe consitpation, fatigue, and cold intolerance, but ZERO weight gain.  My Dr. almost didn't even bother checkig my thyroid b/c my weight was low/normal...thank goodness he did

Definitely at least call your doc, but here's my .02. Last year after my first tri, I was about a month late for my period. Actually bought a pregnancy test and everything, and totally freaked my hubby out. When I start any kind of training that's heavier than normal, I usually have changes in my period. Like Saturday, after riding my bike, thought I'd killed it for the month after a day (had the worst cramps Sunday, but, you know). Also, definitely make sure you're eating enough. So, have you called your doctor yet?

1. Get your thyroid checked. It could be hyper- or hypothyroidism. The menstrual symptoms are similar for both.
2. When I had irregular periods during high intensity exercise, I got a prescription for birth control and that pretty much fixed it for me. Birth control isn't just used to prevent pregancy anymore! :-)