Oh the joys of woman hood! Have you had sex recently? Otherwise, it's just a gush of discharge. Do you do kegal exercises? I would start doing those (where you flex the vaginal muscles like you are stopping a flow of urine). This helps control 'anything' from coming out like that. But would guess it's either from recent sex or a gush of discharge. If you are concerned though, please be evaluated by your physician.
I know after two vaginal births, if I'm straining and say I sneeze, it's gonna be mixed with a little urine. Which is lovely. I know. But very common after childbirth. good luck