Question about beastfeeding and your milk letting down...?

I have a 3 1/2 week old daughter that I am feeding. She nurses off of one for each feeding because my milk supply is great and she seems satisfied after feedings. My problem is...I can just be walking around the house or basically doing anything and my milk will 'let down' on its own. I am wearing nursing pads, but I've heard to change them often to avoid yeast infections and such, but my nursing pads always seems to be somewhat wet. Not necessarily soaking wet, but if I changed them all the time I would have to buy a box every few days! I usually change them 5 times a day...anyone else have this issue with their milk letting down, and what nursing pads do you use? Thanks