How do I get rid of that sour smell?

Assuming you’re not imagining it (because that happens too) I think your skin flora has changed. You can try to reverse this with the selective use of sanitizing soap. We have two types of sweat glands: the eccrine and apocrine. The eccrine produce water with a little salt for cooling. The apocrine make fatty substances to lubricate the skin, including in the armpits, groin and pubic area. These fatty substances are broken down by bacteria into fatty acids – and they often have a strong smell.

Disinfecting soap

You can get rid of the unpleasant odor by showering more often with something that degreases (soap) and later greasing the skin with a pleasantly scented oil. Deodorant contains substances that inhibit bacterial growth and substances (zinc compounds) that react with the fatty acids. Often it helps to choose a different deodorant. You could also wash the armpits and pubic area for a week with antiseptic soap (eg Unicura) or a ‘scrub’ (eg Povidone). Do not continue too long after the sour smell is gone, because eventually the natural balance of the bacteria on the skin must be able to recover.