You are indeed too young to experience this, however, should know the body physiology.
In the private parts, a girl has two openings, one is for passing the urine and the other is for reproduction. This opening to the reproductory organs is known as interoitus. It leads to the vagina inside.
When a girl is getting sexually excited - what you have written as 'sex drive' - there is increased secretion inside the vagina which flows out through interoitus.
Because of the erotic conversation with some one on chat blog on website, as you have mentioned, you got sexually excited without knowing what this is. This increased your vaginal secretions which you saw inside your underwear. There is nothing to worry about this.
You have to refrain from such blogs.
I would urge you to have a detailed discussion with some lady elder to you - may be your mother, aunty, elder sister, teacher or elder friend to learn scientifically about the reproductory life of a woman. This will make you wiser and teach you the physiology and body behaviour of reproductory life cycles. Also you will be well informed about the different risks in this sexual field and will protect yoursef from them.
I hope you take my advice sportively and sincerely before you entre your
puberty.
If any further information required from me, you may contact me directly or ask me direct question also.