Brief, sudden pain on both sides of your lower belly around 20 weeks is usually round ligament pain, from the stretching of the ligaments that support your growing uterus. Duvadilan (isoxsuprine) is a medicine gynaecologists commonly use in pregnancy for exactly this kind of discomfort, and taken as your doctor has prescribed, it's generally considered safe for your baby.
Next Steps
Keep taking it exactly as your gynaecologist advised, and mention any flushing, a fast heartbeat or palpitations if they come up, since those are the more common side effects to watch for.
Health Tips
See your gynaecologist sooner if the pain becomes constant or severe, or comes with bleeding or reduced baby movements.