Sounds like your period to me. The first few periods can be dark brown (old blood), lighter flow. Here is more info for you -
Once you start puberty a white and/or clear discharge is normal - this clear discharge can happen 6 months before she has her actual priods. The vagina is self-cleaning. This same discharge increases the closer you get to ovulation and when you are sexually aroused. Trust me, you don't ever want it to go away. You will also have your own scent - musk like - and smell stronger to you than to others. You can have this normal discharge for weeks, months or even years before getting your first period. It will also continue after you get your period. Wear a pantyliner if it bothers you.
Different Types of Discharge:
White: Thick, white discharge is common at the beginning and end of your cycle. Normal white discharge is not accompanied by itching. If itching is present, thick white discharge can indicate a yeast infection.
Clear and stretchy: This is "fertile" mucous and means you are ovulating.
Clear and watery: This occurs at different times of your cycle and can be particularly heavy after exercising.
Yellow or Green: May indicate an infection, especially if thick or clumpy like cottage cheese or has a foul odor.
Brown: May happen right after periods, and is just "cleaning out" your vagina. Old blood looks brown.
Spotting Blood/Brown Discharge: This may occur when you are ovulating/mid-cycle.
It's ok. Nothing to be embarrassed about. Your mother will be expecting it already. Periods at puberty are erratic, but they will stabilize and soon you will have regular periods. Go ahead, tell your mom