Oh mama, I totally understand why you're worried, a few of us have gone through something similar and it can really give you a fright! The good news is that the Flagystatin vaginal insert can actually thicken and alter your discharge quite a bit as it gets absorbed, so what you're seeing may just be the medication doing its thing rather than your actual mucus plug. Also worth knowing that even if some mucus plug does come away, your body can regenerate it, so it's not always the alarming sign it seems, one of my mum friends had something similar after a cervical procedure and her OB reassured her it was likely discharge mixed with medication residue. That said, since you've just had a polyp removal on top of the infection treatment at only 21 weeks, please do call your gynae or go to the hospital soon just to be safe and get it properly checked out!