Yes, it is good to establish a baseline of your system before you become sexually active. There is a lot of variability in what a person’s “normal” cycle might be, and it does change over the course of your lifetime. A period that lasts 2 weeks might be a sign of problems that are better addressed before you are trying to start a family. It could also be causing you too much blood loss with fatigue and anemia. They will probably ask about family history, so if you can find out about any Gyn issues your mother, grandmothers and any sisters, aunts or female first cousins you might have, it could be helpful.
Whenever I’ve had to deal with uncomfortable situations like a Gyn appointment or getting a massage, I remind myself that this is the person’s chosen career and they see several other people naked every day – skinnier, fatter, taller, shorter, cleaner and dirtier. The Gyn office is used to seeing nervous people, so when they call you in tell them it’s your first time there. If you want the nurse or medical assistant to stay in the room as a chaperone during the examination, it is your right to request that and many women do.