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This could mean problems like hormonal
changes, infection, stress
and similar causes
having white discharge is normal , but if the discharge is noticable yellow all the time and has some bad odor along, then may mean an infection called vaginitis
, due to which the cycles may alter
At your age, hormonal changes are also extremely common and sometimes the cycle pattern may change for a couple of cycles.This is normal.
I suggest you to wait for a couple of cycles, and watch the same, in case the discharge gets smelly with color changes and symptoms of fever
, itch, etc, see your doctor for treatment.