I Have a Skin Rash/irritation in Both Underarms, Can I Get Rid of It? What is It?

I have a skin rash/irritation in both underarms, it's not painful but different to the normal, I had it for about a month, it's about 2cm by 6cm, clear on the inside and red around, it coincides with me starting free weight sessions, is it related? Is it just coincidence? I really want rid of it!

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