Semen or mucus - TMI - no pic

I'm 39 weeks and DH and I had sex last night. About an hour ago I go to the bathroom and there is this thick glob in my underwear. It was thick and sticky but not really wet. I was able to pull it off my underwear without it leaving a trace. Was it mucus plug or semen?? Will semen thicken like that if it doesn't fall out and is up there for a day?