Hello,'Welcome to Healthcaremagic.
From your Query i understood that you have prolonged menstrual bleeding
Usually slight brown discharge after few days of menstruation is normal.
It is due to residual blood shedding in uterus.
It may be due to hormonal changes.
But you have heavier brown discharge and it is also increasing.
It also associated with pelvic and back pain.
Thus it need immediate medical attention.
There are many causes for this prolonged menstrual bleeding.
Some are fibroids or polyps in uterus, dysfunctional uterine bleeding
due to hormonal changes, Infection, Endometrial hyperplasia
Thyroid disease and low platelet count can also cause menstrual irregularities.
In women with PCOS, anovulatory cycle
is common. Anovulatory cycle can cause prolonged and irregular menstrual bleeding.
You may do some basic investigations like Ultrasound abdomen and pelvis to rule out fibroid and ovarian cysts .
Biopsy and swab may be needed.
Do thyroid profile and complete blood count
to rule out the general diseases.
Depends upon the cause, treatment varies.
If it is due to thyroid disease, infection etc.. it can be corrected by medication.
If it is due to fibroid or polyp, Surgical intervention may be needed.
Hope this helps.