How to remove underarm stains and odour

I have a question. What is the best way to remove underarm stains and odour? I have begun to notice yellow stains and odour which will not wash out. I only wear the shirts once before placing in the laundry. I try to do the laundry every week, however that could stretch to a week and a half before the piles get big enough for a load. I have tried, 'spray and wash, and the 'pc' brand stain remover. I have also tried all of the various oxy-cleans. I have soaked for the 10 minutes and even longer for the oxy-clean and still the yellowing and odour persist. I have used Tide, Sunlight, PC brand and am now using ECOS, which is a green product.

I have been advised by some people to change my deodorant as the aluminum content is causing the yellowing. What do you suggest? I would like my clothes to look and smell clean after I wash them. Is is the deodorant or my diet or age (Carolin, I'm not harping on my age, I'm just wondering if this is a natural occurrence, chronologically speaking).

Please, any and all advice is gratefully accepted.

Thanks