My daughter has been through some extensive testing due to her periods not being regular. However she does suffer from a chronic illness as well that has thrown her off schedule.
However I will share with you what we have learned.
It can take 2 to 3 years for teenagers periods to become regular from the first time they get them.
It is NOT uncommon to be regular for a long period of time and than all of a sudden to be irregular and miss peiods. Even as many as 6 to 9 months worth in those first 3 years from your first period.
When they say NOT uncommon they also mean that most likely you are hearing from your teneage friends that they get theirs each month regularily. However it is still NOT uncommon to miss them so do not feel you are not normal if you do become irregular.
It does not take much at all in the from of stress from a teenager to make a period become irregular. Being a teen is stressfull so irregularity is going to happen at times for most teenge girls.
If you go 12 months without one than see a GYNO to let him/her know whats been going on.
Okay than....I hope that helped.
Now as far as a big bite on your nipple goes. Of coarse you can get a bite there. You can get a bug bite in any place on your body. Some more uncommon than others due to being covered with clothing. However it is still possible for bugs to bite through cltohing.....anywhere on your body.
As far as a third nipple goes. I have known 3 people in my lifeitme to have had one. Two being women one being a man. Only one of the women had hers removed becuase it stuck out like a nipple does. The others were flat like and below the breast and thye were not concerend with them.
Plastic surgeyr can remove tham...it is a persons own choice if they feel they would like to go that route or not.
Good Luck to you