Old blood?

How much old blood/brown discharge is normal? Today I've had quite a bit of it and kinda freaking out this will be my 4th pregnancy and never had this problem. Everytime I use the bathroom today I get about the same amount. I've posted this before but with my pregnancy test. And I'm honestly just terrified. I've been having lower back pain and uterus cramps my first dr appointment isn't for another 2 weeks. 😖