I was under the impression that babys under a year do not self-wean (not that I think you are suggesting that, per se).
I don't know if this is helpful, but kellymom says:
"When a mother says that her baby self-weaned before a year, there is a
chance that she interpreted a normal developmental stage (perhaps
combined with her own wishes) as baby’s wish to wean. Low milk supply
can also play a part."
It may have more to do with developmental changes and that this is just a part of it, not baby weaning or low milk supply.
As for pumping, namara suggested what I did when I needed to produce more: fenugreek, oatmeal. Also, by increasing the number of times you stimulate your nipple (i.e. nursing/pumping more frequently) you can increase your milk production.
I wish you luck.