Spotting/Back pain/Light cramping

I’m around 5 weeks and I was experiencing very light brown/clear spotting the first couple days sporadically, tonight I wiped and noticed it was much darker looking. I also have dull back pain, but I’ve been at the vet for 3 hours with my cat so it may just be from sitting in same position. A little worried. Has anyone else had discharge like this? Hoping it’s just old blood from the period I didn’t get