I feel itchy after running and when riding a motorbike?

I feel something strange with me since two years ago. Sometimes, not often, I like to go for morning or afternoon run in a yard near my house. It's still natural with trees and soil. I wonder I begin to get itchy in my whole legs but not the body. It's nothing wrong with the detergent or allergy since I didn't get this itchy before. Another itchy moment is when I ride a motorbike and found my belly get itchy as well. Any advice?