Bleeding - what does this mean?

Suhaifa • Pregnant with Baby #2 | Attempting VBAC
It has been 3 weeks since conception and my HCG levels are very low, increasing but not doubling. 
Today I had some minor cramps and bleeding. The blood is very light pink and diluted almost. It's not visible on my panty liner but only when I wipe.
Could this be implantation so late or miscarriage?