What Causes A Knot Next To The Opening Of The Vagina?

I had a knot just next to the opening of my vagina that I noticed after giving birth to my 4th child. It was still there by my 6 wk checkup. I'm now 3.5 months postpartum and I noticed small amounts of very thick mucous discharge sporadically when wiping after using the bathroom, and now the knot is gone. Could it have been a Bartholin gland cyst and could the mucous have been from it rupturing? The knot never caused any pain at all.