Sustained supply drop

Hi! Happy Mothers’ Day! I have been EBF with my 7-month-old with a combination of direct feeding (4-5x/day) and expressing with Spectra s2 (2x/day, first time 1.5 hours or so after first feed, second time just before bed at like 11pm). We dropped the midnight feed when LO was 1 month or so. About a month ago I took plan B and had some heavy (by my standards, so not very) bleeding then, which tapered off after a few days.

My period is now more than a week late. The volume I’m getting from that expressing session in the AM has been decreasing steadily, I think even from before I took the plan B, though it certainly seems to have ramped up since then. Today I only got 0.25oz combined, when usually I get 4-7oz.

I’ve replaced the valves to eliminate that as a cause also. I took a pregnancy test last weekend which was negative. I also took plan b several months ago and did not notice any bleeding then, nor did it seem to impact my milk supply as much. I also have not really experienced as much bleeding when taking plan b before the pregnancy. Has anyone else experienced this with plan b? Could my supply just be drying up even though I am doing 6-7 removals a day bc of baby’s age? TIA!