Hey just to let you know..vitamin d isn't like...something you can get dependent on or "stop working". your body needs it sort of in the same way it needs air and water, just not to the same extreme. It actually does function like a hormone though, which is part of why it is important. Getting a blood test @ the doctor might help alleviate some of your anxieties, you can get your vitamin d levels checked and if you're low, that's prolly not helping your mood. and also there are many other important health indicators they can check, including hormone levels. Also vitamin d has nothing to do with getting pregnant, except for the fact that it would logically be better to have adequate levels of vitamin d when you get pregnant for overall health. just like it would be beneficial to be adequately hydrated throughout a pregnancy. you can take vitamin d supplements, which I do, but sun is probably superior in a lot of ways as long as you don't stay out too long and get a burn. i think half hour direct sunlight everyday is "recommended".
I got really upset when I was having pcos symptoms, acne and lack of period, but it's really nothing to be super upset about. as far as body disturbances go, it's very low on the list of traumatizing things. of course if you've had heavy symptoms for a long time, that will be a little harder to treat, but if this is a more recent thing, you can get control over it easily. have you seen a doctor recently?
I second everything the above poster said about diet. It's all about complex carbs, lots of vegetables, and whatever sources of protein you like. and fiber. and not having massive anxiety around food or isolating yourself because of it (aka cutting out a whole bunch of stuff). you're already at a low weight, so restricting carbs is really hard. i'm 5'8, 132 lbs and I felt so horrible trying to cut out all carbs (including fruit) awful awful awful.
Birth control was a great, "easy" fix for me...I felt life was too short to spend the next x number of years trying to balance my hormones with a naturopath charging me a shitload of money for herbs. my family was looking at me like wtf and they are very progressive and liberal. not saying theres ANYTHING wrong this alternative treatments, just explaining. for me, birth control (ortho tri cyclen lo) cut sugar cravings by a lot (pcos symptom), gave me more energy, made me feel like "myself", basically made me stop feeling like shit. this helped propel my health in new directions once I had the energy and normalcy to function optimally. but yeah, some ppl hate birth control or don't believe in its uses, so follow your heart