Lomelly I wouldn't be too concerned as brown indicates old. It could be from a previous bd session or maybe you were straining more than normal? Here is what I found on a med site:
Vaginal Discharge
As the pregnancy progresses, you may notice you have increasing vaginal discharge. Typically it looks like egg white, is milky and a bit odorous, and it may remind you of premenstrual discharge, only a bit heavier and more frequent. This discharge is absolutely normal and is just another change your body goes through in response to the pregnancy hormones and the increased blood flow to the area. You can wear panty liners or change your underwear more often than usual if you find the discharge bothersome.
Though the kind of discharge described above is normal, there are some types of discharge that may mean you have an infection. You may have a condition that must be treated:
if the discharge looks like pus;
if it is yellow, green, or smells foul;
if you notice a burning sensation when you urinate; or
if your labia are red, swollen, or itchy.
Vulvovaginal candidiasis (yeast infection) is very common during pregnancy. Signs include a thick, cottage cheese-like discharge accompanied by itching, redness, and burning, as well as painful intercourse and urination.
Sexually transmitted diseases (STDs) may also occur during pregnancy, and because many of them can affect the fetus, it is important that they be treated.
Try not to panic I think you are just fine. Dr. Ready reporting! lol