Is she spitting up a lot after each feeding? I had both OALD and I still deal with OS from time to time when Peter chops and changes his night feeding from sleeping 8 hours straight to waking every hour. It's hard for my poor breasts to know how much milk to make!
When Peter was younger, I could tell I overfed him when he spit up a lot after each feed. Sometimes he would spit up 10 times over 2 hours. I realized that I was just producing too much milk for his little tummy to be able to handle. This caused a lot of discomfort on his part. You know what it's like when you overeat....sometimes you get very uncomfortable.
The crying while nursing is usually a result of OALD, and I had that. DH thought it was pretty cool that I had a self-spraying boob. Sometimes, however Peter would start screaming in the middle of nursing and it turned out to be gas pains. I only realized this after I posted a similar thread 8 months ago and one of the Mom's suggested gas pains. To help ease any discomfort as a result of gas pains, I would move his legs like riding a bicyle and scrunch them up and down into his abdomen. This usually helped him to feel better. OALD causes gas, as babies tend to gulp, gulp, gulp, often taking in too much air. Leads to a lot of burping and general gassiness.