A breast reduction can certainly dramatically affect yor ability to have enough milk - it depends how skilled your surgeon was in preserving your ducts.
Was it the classic anchor reduction you had?
I've also had a reduction. My dd is ebf. She is my second DC. DS had to be mix fed for a while - both my children have tongue and lip ties, and DS's was missed. He couldn't stimulate my milk supply, which was perilous due to the reduction anyway, and he was generally not arsed with feeding, so it was generally just a bad situation.
With dd I had already done all my research thanks to the horrible experience with DS losing weight and having to mix feed. Here are my tips:
Allow him unlimited access to the breast.
When he isn't at the breast, pump ten minutes on each side. If there is milk there, pump 10 mins after your last drop of milk.
Take yourself to bed and do nothing but feed, express, and sleep.
Try biological nurturing - this can aid in a better, deeper latch to increase milk transfer.
Do breast compressions.
Check for lip and tongue tie - don't trust someone else to do it for you. Look for Laurence kutlows presentation and check for yourself. Health professionals in the uk are woefully inadequate at identifying ties. As I said, both my children were badly tied. Both had the ties missed, by midwives and paediatricians at 2 different hospitals each. Luckily, second time round I had the confidence to say they we're talking shit and get it sorted.
How is your latch? Are your nipples sore at all? Are his poos nice and yellowy?
If you need any more help/advice regarding feeding after a reduction, feel free to pm me. Dd is now 16 weeks old and has never had a drop of formula. :)
(Also, there is a growth spurt around now that you may be in, accounting for the cluster feeds).