6 wk old feeding and eating every 1-2 hours?

When my 6 week old was born, days later she began "cluster feeding" for almost 2 weeks. If you don't know what that is, that is when the eat every 20, 30, 45 minutes. I had ALOT of milk producing at that time. She slowed down her feedings to about once every 2-3 hours around the 3 week mark. Starting last week, she started eating again about once every hour to hour and a half. I read that this could be that she is going through a growth spurt? Also, I normally pumped because my body was producing so much milk, and had SOOO much extra to spare, but now it seems I only have enough to feed her at her feedings. I wanted to pump extra so I have milk to feed her while we are out. So I guess this is a 2 part question: is all this feeding a sign she could be going through a growth spurt, and 2. what would cause a decrease in milk availability to pump? thanks for your answers!