It could be your mucus plug. I personally lost mine with my first baby in 2 big slimy chunks in one day the week before I was induced. But, some people lose it over the course of a few weeks.
It might could be semen, but usually that comes out pretty fast after sex, unless you are laying down for a long time afterwards...I used to go to the bathroom right after we did it and sit on the toilet and wait for it to all come out...LOL Well, not when we were TTC - at that time, I'd lay on my back with my butt up and hope mother nature brought it where it needed to go! ;-)
We don't have long now...hang in there!! :-)