Pregnancy 21 weeks. Twins naturally. Brown or light brown discharge at…

Pregnancy 21 weeks. Twins naturally. Brown or light brown discharge at times. My gynecologist prescribed progesterone suppositories three times a day. It's very painful to walk, but the children are very active, even through the pain, they keep poking each other all the time. Are there specialists in twins who can answer why the discharge? Ultrasound showed that everything is okay. But I can't lie down, sleep and walk normally, it hurts very much like during menstruation.