The first thing to remember? Don't panic! Dolly Doctor confirms that everything sounds completely normal.
It's great that our reader felt comfortable using a mirror to try to see and understand what's happening, particularly in the genital area - we recommend all girls do this if they can, there's really nothing to be afraid of!
The "hole where your period comes out" is your vagina.
In the female anatomy there are three holes in the genital area: the vagina is the biggest, the urethra is where urine comes out and it's above the vagina and under the clitoris.
The third hole is the anus, which is around towards the back and is of course where poo comes out.
The vagina is a muscular "tube" that is normally "collapsed down".
When you look at it in a mirror it may not even look much like a hole. You can spread apart your inner labia (inner lips of the vagina) and get a closer look, you can even gently insert a finger to see whether you're noticing a flap of skin or whether the walls of the vagina are just closed together.
Right at the opening of the vagina sits the hymen, which is a piece of skin-like tissue and this is what you might be seeing.
All girls and women will notice something a bit skin-like if they look closely. The hymen has a hole in the middle of it which grows and stretches as you grow, especially during puberty.
Usually with the use of tampons the hymen simply stretches without any problem, If your hymen is particularly thick, and the hole in it isn't stretching as easily, you might have a bit of resistance to inserting a tampon.
Try inserting a clean finger right inside your vagina, and try a small tampon, while using the mirror, to see whether you can gently stretch this area.
You can use Vaseline or lubricant to assist (though don't when you actually have your period).
The difficulty you find inserting tampons may have nothing to do with the hymen, as most girls do need time and practise before they can use tampons easily.
Often it's more to do with inserting the tampon in the right direction — up and back towards your belly button (you might need to lie down, or to stand straight up with one knee bent and that leg up on a chair, or squat).
And of course if after all of this you still think that the piece of skin you've noticed is obstructing the entrance of your vagina, you can get it quickly and easily checked by your doctor.
Got a question for Dolly Doctor? Send us an email and we'll get it answered! email@example.com