Nothing to worry about, and it's probably not your plug.
You can try to do a google image search to see if you can find a picture of one.
"mucous plug"
Most often it has blood streaked in it (brown or red) and it is a little thicker and more gelatinous than regular CM.
Your cervix is making a lot of CM to maintain the cleanliness of your vagina to keep infection out. And the weight of LO may be making it easier for CM to exit your body sooner than usual, so it looks different that what you normally expect.
I know when you've not had one before it's hard to know what you're looking for. Its kinda like trying to describe braxton hicks contractions vs. real ones. First time mama's always want to know the difference. The best answer is YOU'LL KNOW.
And generally speaking YOU'LL KNOW when you loose your plug. If you have a question it's probably not it. But certainly give your doc a call if you're worried, and experiencing pain with this.