What Causes Formation Of Scab On Leg And Underarm?

Hello,I am 27 years old, last week a notices what i though was a bite on the very top of my leg but was not itchy. i quickly turned into to a scab and is getting bigger, since then keep finding more i have one on my bottom now a few on my under arm starting turn scaby i have now found some starting starting on my other under arm.
Do you have an ideas what this could be or what i could do to stop any more appearing?