27 years weak n my period enjoy last 16-18 days for the second 6 months?

could it be a sign of something bad?

Answers: yes! GO TO THE DOCTOR. NOW.
lol sry but nearby might be a chance you hold a cyst or even a fibroid because there is no grounds why it should last that long.
but if u are on the pill that might hold something to do with it

u may involve some estrogen...talk to ur doctor