are you having problems with excessive sweating? if so, that might be the cause of the problem. from what i've experienced, i had a problem with too much sweat, i use Certain-Dri anti-perspirant (it comes in a box) and you can get it at wal-mart or a drug store like walgreens for about $6. it helped me with the perspiration, which then controlled the smell. i just use it at night before bed, and then use a regular deodarant during the day---no problems for i think 4-5 years. highly recommend it. also i've read to use an antibacterial soap like dial on your armpits when bathing to remove bacteria that causes foul odors. as far as it not being caused by too much sweat, i can't help ya there.
good luck, hope that might help some