Why Is The Mole On Skin Sore And Itchy?

Hi, I have a mole on my leg that has become angered. I cant recall knocking it but over the last couple weeks it has became sore and sometimes itchy, The mole has half of it covered in what looks like a scab and the other half is very tender with a blood like substance coming out now and again, Is there any over the counter creams for this, Many Thanks, Paul.