What Causes Itchiness Of Nipples,and Yellow Discharge During Periods?

I am 18 years old, 165cm tall and 50kg in weight. Ever since I started having my period at 11 years old, I get sore and itchy nipples (usually on the right side but now also on the left) when my period starts. I get clear discharge too that hardens into a yellow fluid that sticks to my clothes. Sometimes, there is blood. But the symptoms always go away after my period ends. What is this?