Thanks for posting
Brownish red spots that occur during menses can be normal.
But there is the necessity of ruling out any vaginal infections that could be responsible for that.
Having stains on your underwear could be as a result of leucorrhea which could be pathologic or just physiologic (normal).
You will need to consult with a gynobs so you can properly be examined and maybe treatment for your menstrual irregularity can be started. Metformin
is well indicated for someone who is overweight
and wishes to loose weight. Overweight can also be responsible for the irregular menses.
Wish you a better health