Breastfeeding problems! Help please!!

My 4 day old seems to be spitting up big amount of breastmilk after every feeding. I think it may be because I have an oversupply. Anyone deal with this? She tends to gag during a feeding because of my fast let down, so I have been trying to do the laid back nursing position and hand express milk before her feeding. It doesn’t seem to help. While she is nursing on one side I will leak 2 oz in a milk collector from the opposite side. I nurse every 2-3 hours. She doesn’t usually want to nurse on the other side after she has finished either, but the pediatrician kept saying to nurse 10 minutes on one side and 10 minutes on the other, but she never wants the other side and only nurses for about 10 minutes on one side. Is any of this normal? Any tips?