Well from my experience in College Physiology and Anatomy, I'd say the irritated mucus sarcolema or maybe the lining of the lungs becoming in need of oxygen, your body then taking in more air (drys the mouth) resulting in a coppier taste also described as blood because their is less mucus to cover the actual tiusse

Regradless just bring some water and run more! Nothing to be worried about unless you see or cough up blood. The itching knees is probably due to your body reacting to the running, take some benadryl (capsule) about a half hour before running, it's a anti-hystameine, meaning it will cause a reduction in sensory feedback(itching

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