I have some personal experience managing overactive MER-- it took me three nurslings to get it right-- and I have helped several mothers with similar situations. Given the short feedings, the vomiting and the shooting pains, I think you are right to suspect it. Overactive MER can very easily create an oversupply problem (baby vomits entire feeding (sometimes at each feeding), then has to be fed a second time). I would be wary of pumping or anything else which might increase supply. The shooting pains in breast can often be explained by rapidly refilling milk ducts.
    The best strategy for me and mine turned out to be this: watch for the letdown, as soon as letdown occurs, break the suction and catch the stream with a cloth diaper (keep holding the breast the same way you were when nursing, eg, C-hold, U-hold, etc). When the letdown subsides, and no milk is shooting out, put the baby back on. Very soon, the baby will learn to stop nursing on her own when the letdown starts and resume a short time later. Very simple, but effective. Once the baby stops vomiting, the oversupply problem should take care of itself. If it doesn't, some mothers find that nursing on one breast per feeding helps.
    Good luck!
-Arlene,

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