Lost weight...and my period

You need to be getting enough fats for periods to happen normally, so if you're doing low fat, don't. It also could be stress, so try to avoid that. Other than that, your body may just not like being that small (at six feet you should probably weigh a bit more I'd say) so try eating a bit more (maybe 1850 or so) and see what weight you maintain on that and how your body reacts

If you are on BCP, could be a side effect of the drug. I would check the info packet and talk with your doctor first and foremost.

Glanced at your diary.... your goal is 1800 but you usually fall short of your goal by a few hundred calories. Try to actually eat 1800 every day and see if that helps. It could also be an effect of BC depending on what kind you take. And of course, you've probably considered this, but is there any way you could be pregnant?

1300 cals a day is too little at 6 feet tall, so I wouldn't be surprised if that just threw your body off and it's taking some time to adjust back to normal. If nothing changes though I would see a doctor to be safe.

It could be a lot of things. Firstly birth control has A LOT of side effects that can come on at any point. I unfortunately found this out the hard way when the depo shot nearly killed me. Of course, I am going to suggest you take a home pregnancy test because 3% of people still get pregnant on the pill. That would be the first thing I would do if I were you.
Secondly, maybe increase your fats a bit if you're doing ultra low fat, as other posters have said fat can help regulate your menses. I calculated your BMI at 19.5 so I don't think you're underweight or atrisk of that.
Stress also has an amazing ability to make aunt flow disappear so try to relax and if in 1-2 months your period still doesn't return I would really consider going to a doctor, if not sooner if you can afford it, but a lot of doctors will throw it down to stress unless something is wrong with you so be prepared for that frustrating conversation.

I with you the best and way to go on the weight loss!

Yep, happened it me 2 years ago. I am 5'3 and went from 134 to 125. I lost my period for 6 months. You need to eat more. After I put back on about 7 lbs it came back! I'm older than you (37) and done having kids.

See a medical doctor!

You lost it most likely because you are eating at a calorie deficit therefore you are not eating enough to fuel your body so your body is going to stop any unnecessary "calorie expensive" processes that are not vital to life, such as reproductive processes. I have lost my period at different weights/body compositions and diets, the only thing that has caused me to lose my period was eating at a calorie deficit. So you just need to eat more to make sure you're properly fueling your body and your period will come back eventually.

It is a somewhat common thing to happen with weight loss. I had a 60+ day cycle after losing 25 lbs. and my OB/GYN said he would have been more surprised if my period had not been affected by the loss. And yes, I was getting plenty of fat and calories. Still, you should see a doctor just to be checked out.

OH PA-LEASE with all the "eat more fat" crapola. She needs to SEE HER DOCTOR. We shouldn't be handing out medical advice. OP, see your doctor, because this could be caused by a myriad of things, and no one here can speculate with any kind of accuracy.

Agree with the above post. Truly, when you are on birth control, you do not have a "true" period, due to how the birth control works. I am not going into details here, as you should ask your doctor about this.