Ruf, right thru the last trimester, it's common to loose bits of what U think is ur plug, and may well be, but it's snot like and I lost a lot of it off and on right thru. I never worried as I knew whatever I lost would replace itself. The only time to really panic is if u loose it with heavy cramping or u think ur waters have broken. The plug generally looks more solid and like a chunk of solidified fat/jelly. White in colour and maybe some blood. A bit of a show is more runny snotty like. It is also common to loose a lot of CM during the third tri. I often had heaps and heaps of cm run out. HEAPS AND HEAPS. Usually it was when I did a poop (sorry tmi)or after sex (like 6hrs or more).
Get it checked out hon, but try not to panic. It's all very common and normal honey. As I said, only panic if u start cramping or u think ur waters have broken. Goodluck hon, and I am so excited for you and happy for u! *hugs*