I know some women end up with more discharge then usual with pregnancy. I am one of those that produce more discharge when pregnant and this is my third. But if it is yellow then you might want to go in and get checked out just in case. Definitely don't think its your mucus plug cause that's more sort of brownish red nasty looking.
I'm 29 weeks and I had a very similar thing today. It wasn't normal discharge...mine wasn't yellow but kind of clear. I'm curious about the aame thing, mine was a good tablespoom amount.