Brown discharge?

So today I was at work and thought I started my period(not due for 4 days). When I got a chance I ran in the bathroom went pee and wiped noticed it was brown with light pink in it. I put a pad on real quick and didn’t get a chance to check anything again for like 6 hours.

When I got off there was only maybe 1x1/2 inch of brown blood and literally no more since. I had mild cramping and super sore breasts and completely exhausted (sleeping 10+ hours)

I just went to the bathroom again and when I wipe it’s super brown with a little red. Still having little cramps here and there.

I’m 24, my husband and I never use protection, and haven’t been on bc for 8 months.

Is it most likely old blood or implantation bleeding?