You're only 17 so this is very common at your age. You're body is still growing and going through puberty so irregular cycles can be quite common. The will hopefully regulate themselves soon enough. If you're concerned, see your doctor and they should be able to give you something to induce your period and hopefully get your cycles on track.
best thing that you should do is to see your doctor for examination.
missing a menstrual period when you are not pregnant is called amenorrhea, which is the technical word for absence of menstrual periods.. in women who are not pregnant, it is usually due to a hormonal imbalance. while these hormonal imbalances are not usually serious, there are some long-term health risks that can be avoided with treatment. understand that missing a period is neither a disease nor a sure sign that you’re pregnant. sometimes missing a period is perfectly normal and doesn’t mean anything is wrong.