I know throughout your pregnancy your mucus plug comes out and grows back but last night I was…

I know throughout your pregnancy your mucus plug comes out and grows back but last night I was having really bad pain on one side of my back not my normal back pain & I was hurting down there as well & very uncomfortable while I walked because of the bottom of my belly & today after I wiped on the tissue there was what I believe was part of my mucus plug... But baby is active moving at all times of the day. What can it be ?