Can zoloft (sertraline) cause heavy painful period?

Yes: Zoloft (sertraline) is in a group called ssri's-, used for depression, which is much more common in women; the depression, or irritability, mood disorder, anger often occurs premenstrually. These ssri's can definitely cause changes in menstrual cycle--inc bleeding, pain, irregularity. A successful way of treating premenstrual depression is taking zoloft a week, starting 2-3 days before it starts.

Possibly : Per Drugs.Com Sertraline can cause menorrhagia (heavy period ) in less than 0.1% & menstrual irregularities in general in 1 to 10%. REF: https://www.drugs.com/sfx/zoloft-side-effects.html