Pumping and increased bleeding

I am 7weeks pp, I exclusively breastfeed with the occasional bottle when we are out in public (of expressed breast milk), my bleeding stopped around 4 weeks and within the past week and a half I noticed slight spotting like once a day, but when I pump (usually once a day, just to create a small stash) the bleeding increases and fills half a panty liner. I was wondering if anyone else has anything similar happen to them?