It is most likely a hormonal imbalance causing irregular bleeding. The common causes are stress, changes in diet, workout routine, any new medication, Infections, Plan B, Recent illness, fibroids, or sometimes ovarian cysts. Usually, it settles on it sown so just wait and watch for 1 to 2 weeks, the cause is most likely the depo shot which you started in sep.
It can happen occasionally and nothing concerning as it is a self-settling condition.
Meanwhile, regular exercise and cutting on carbs would help.
Taking Ibuprofen 800mg thrice a day for a few days would help with bleeding.
Nothing much to worry about.
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