has this happened to you?

so I went to the bathroom after having sex and when I wiped this is what I saw. it was this goop mucus like stuff and it had a redish brown color. he did not cum in me at all during sex and I just took a test for pregnancy and it said negative. the only time I have had this happen was when I was pregnant and lost my mucus plug, but it was more clear and had red tinge to it. Has anyone else experienced this? Any ideas as to what it is?