Emm I honestly culdnt tell u, mayb u shuld use a different soap powder n if the smell is still there then it mite b ur washing machine.......mayb theres a sweaty sock lingering in there :p
Years ago there was a rash of complaints that Ariel washing powder was making clothes smell like dog pee. Many people disagreed. No conclusion was reached, but it might have had something to do with the mineral content of local water supply reacting with ingredients in the powder. Just try a different detergent. If the smell's still present, try a different fabric softener.
I always spray underarms and shirt collars with a pretreatment such as biotex, I also add adritt oxypower to the wash. This seems to get rid of the bacteria that causes bad smells. The other things that you might try is buying one of the washing machine cleaning products and ive that a run through, i think vanish do one.