Hiyer,
I had 12 months (but not as long as you) of no period at around 30 years old, it was a hormone imbalance....caused by nothing much but a hormone imbalance lol I was in the midst of a big anxiety episode with a hospital stay at the time it stopped. It righted itself over the following months. It really, honestly could be that simple. I know you are going to think the worst, after all that is a long time to have the ongoing issue, but I think if it were anything more serious or sinister you would have known a long time ago with lots of other symptoms. You have mentioned some symptoms, but those could be attributable to some simple easy to deal with issue and I think some mild headaches, acne and floaters in the vision (is that what static vision is?) don't sound that unusual for anyone of 18 years old.
I think you are very sensible going back to the doctor, and I hope you get some bloods done for hormone levels, along with thyroid and a few other checks. There can be many many reasons for amenorrhea, but the most common ones are stress, excess exercise, very low body weight causing hormone imbalances, thyroid activity levels being off kilter and yes of course PCOS. (WHICH is treatable!) Don't jump to the most unlikely scenarios, because doctors don't when they see you, they start at the most likely and simple.....
BY the way, if you also have anxiety problems, they could also be caused by a hormonal imbalance. You don't mention if there was anything that occurred before the periods stopped ?
I just found this information on an article.....
Most of the time, irregular periods are part of the normal changes that can happen when you're a teen. At some point as you get older, your cycle will probably settle into a recognizable pattern. This usually happens by 3 years after your first period.
However, some teens may develop irregular periods — or stop having periods altogether — as a result of certain medications, excessive exercise, very low body weight, or not eating enough calories. Others may develop problems as a result of a hormone imbalance. For example, disorders of the thyroid gland can cause menstrual irregularities if the levels of thyroid hormone in the blood become too low or too high.
Some women have irregular periods because their bodies produce too much androgen, which is a hormone that causes increased muscle mass, facial hair, and deepening of the voice in males and the development of pubic hair and increased height in girls. High amounts of androgen can also cause hair growth on the face, chin, chest, and abdomen, and is sometimes associated with excessive weight gain.
If you have any of these problems, or if your periods are irregular for 3 years or more, see a doctor. The doctor may prescribe hormone pills or other medications or recommend lifestyle changes that can help you to have regular periods.