Producing milk but struggling with letdown/pumping?

My baby will be 3 months next week. Initially, we were bottle-feeding and breastfeeding and had built up a stash, but our schedule has been all over the place recently, and we kind of naturally moved towards mostly breastfeeding.

My supply has dropped (probably regulated)…I have plenty of milk and would like to pump more, however, the pumping is only mildly successful now. I have never had problems pumping-with my first baby, I almost exclusively pumped. Plus, at the beginning with this baby, I was pumping anywhere from 8-12oz (which was way too much and I fixed that)! Sometimes I get 1oz, 2oz, 3oz…but other times, I can pump for 15 mins and get nothing, even though the milk is there (I’ve tried to hand-express and it works, but takes a lot of work for a little).

So this is a long way of saying…what do I need to do to help with letdown, if that is the issue? Could the pump be the issue? Thank you!