There are several possible causes for this several of them have been mentioned by others, first I would ask when the last time your regulators where benched, cleaned and serviced by a QUALIFIED tech. You may have some Mold build up.
The next question would be the Tanks are you diving rentals? or your own.
If they are your own I would have them cleaned professionaly and re inspected, if your diving Nitrox or tri mix you are at a higher risk of internal contamination if the tank(s) are not properly cared for.
If all those suggestions are in good order I would suggest that you call DAN (Divers Alert Network) and discuss your situation in depth with them.
If you want to discuss in further detail please send me a good contact phone number in a private e-mail and I will try to help you sort this situation out.