What Causes Rash On Legs After Taking 'azithromycin'?

I was treated 10 days ago for Chlamydia (1000mg azithromycin). 4 days after treatment, I developed several canker sores,as well as a rash on both legs (shins). The canker sores have since cleared up, but the rash seems to have gotten worse. Could this be a reaction from the antibiotic? And if so, should I go back to be retreated?