Tablets are made to a formulation, like a recipe. Sometimes the "recipe" is a bit different between manufacturers, or I guess in your circumstances the slow release.
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It would definitely be worth asking your Doctor if you could try a different brand. The prescription can either be written stating along the lines of "Do not dispense X, Y or Z brand", or alternatively, once/if you find a brand you tolerate the prescription can state to only dispense X brand to you.
I have this situation with one of my thyroid meds, where one brand makes me very nauseous, but most others are OK.