Breast feeding idk what doing please help

I had my baby on the April 3rd , my milk supply has came in today on full demand I could probably pump ALOT of milk in one go . The lactation consultant said for me not to pump all the milk out because that make my body think it needs to make even more , and baby decides he only wants to use my left breast he’ll latch to my right but not for long or long enough to really get relief even if I start on that side so I’ve been pumping at feeding time for about 3-5 mins but my boobs are so swollen and it really hurts how do I help it and how long does this last?