37 weeks brown discharge?

Last night my SO & I had sex, afterwards I went to the restroom and wiped and there was a bit of light pinkish blood, but I thought it was just from friction. Today I had terrible lower back pain and so much pelvic pressure when standing and walking & I went to the restroom to see this in my underwear this afternoon, as well as before bed it’s still coming out brown. Anyone know what it could be from or if I should worry?? Baby has been moving all day so I know she’s okay