I have dark underarms. What concentration of glycolic acid peel/cream should I use to lighten them? (Photo)

I have gone to 2 derms in the past and one said it was acanthosis nigricans and the other fungal infection. I think its the former because my skin looks thick and the anti fungal powder and lotion did not help. Im using a 20% urea cream which has helped but hasn't restored my normal tone. Ive also started using kojic acid soap since last month and that has helped a bit. Now Im considering using glycolic acid cream/peels. Will it help? If not, should I use higher conc urea cream?