My body odor has changed in recent months and is now strongly sulfurous. Why might this be?

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Sometime in the last 6 months my body odor began to change. It has shifted from a musky smell to a more acrid sulfurous/onion smell. The most significant change that has occurred in this time has been moving in with my girlfriend. Even if I scrub my armpits very well with soap and hot water, the smell will often be there almost immediately after showering. Thanks, Ben