Emma,
I don't know if I have an over-supply. How much is 'over'? When I pump at night (3-4 hours after last feed), I usually get 4-6 oz in 10-15 minutes. I don't think my let-down is really fast, either. I never spray or leak.
I think he is gaining alright. His birth weight was 9lb 13oz, and I weighed him at home last week, and he was 17.5. I don't know the rate he should be gaining at, but he is gaining!
The problem with him spitting up so much is that I am always afraid that he is not receiving all the nutrients he needs. I got our routine all goofed up because I kept feeding him after he spit, which made him a snacker, as he spit up ALL the time! Now we are on a 4 hour routine, and he seems satisfied, but I still worry!
Carly