long time to get letdown...

I posted a few days ago about my son pulling off the breast, and I couldn't get him to nurse. I figured it was because he was used to the bottle because we had just recently gotten back to breast.

I've been offering every feed, sometimes he will nurse, sometimes not. I've noticed when pumping it takes almost 5 min to get a letdown, it used to be almost immediate. I still get the same amount of milk, but it takes 20min to empty instead of 15. Why is this, any ideas? I think this is why DS has been so frustrated!