oversupply HELP

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Hi I believe I have an oversupply and a heavy let down which is causing my baby to fuss and scream while feeding and never really get satisfied. He's nursing every 1 1/2 for long periods of time and it's wearing me out. He won't nap long either and he seems like the gas is causing his pain. 
Anyone have this issue? Can you shed some light as to how you helped your baby? Thank you!!