Hmm the underweight part can also highly contribute to shorter light periods ir none at all. Basically creates lack of estrogen. I am a recovering anorexic. I was not total bones but kept my weight below enough for so many years that I ended up with more damage than one might figure. In the last few months I have developed stress fractures along my shin. Result from being underweight, low estrogen production which creates terrible bone density. Eventually osteoporosis. This is linked to anemia as well as a contributing factor. Basically I'm just saying that if you leave these things they can cause major problems.

I'm not american, not sure if you are ..so I have little knowledge of how to afford medical help when you need it in the states. I would think there would be some way around that issue but I wouldn't have the slightest.

Well keep a watch on your following periods and hopefully this may resolve. Periods can fluctuate quite a bit over time. Kale if you dont eat it is amazing for iron and amazing for other nutrients..you can't really beat it. And its not expensive. I would not add iron supplements without knowing where your iron level is as that can be quite dangerous. Other than that maybe try to bring your weight up a little if you can..I dont know the circumstances around your weight but suspect that is the root of the problems.

Hopefully someone else can be more useful about the medical care part..