HI, thanks for using healthcare magic
It is understandable to be scared but you should always tell your mother or another grown up about any worries you may have. They can only help if they know.
At your age, periods can be irregular, it is not uncommon, they may regularise as you get older.
The thick yellow discharge that you are seeing may be a yeast infection. Some females have yeast infections
with their periods due to the hormonal
changes that occur.
These infections can also be associated with vaginal itching
You should consider consulting your mother, she would know how best to help you. Most women have experienced yeast infections.
I hope this helps