Mucus plug At 20 weeks

So I went hospital today because last night I had a massive amount of thick discharge with blood and the discharge has since gone clear but still very thick and snotty like SORRY TMI

I went hospital they did some tests and told me ‘don’t worry if it’s your mucus plug you have a cervical cerclage in place that looks very tight’

I thought losing the mucus plug meant labour? And if it isn’t mucus plug what is it? Doctors didn’t seem at all concerned about it just because I still had a stitch

Anyone else had a similar experience or advice?