What Causes Wet Coughing With Severe Knee Pain In Children?

Hi, my 4yo son woke up with a barking cough 2 days ago and a complaint of his knee hurting. The cough has progressed to a wet cough, he now has light sensitivity, and the knee pain is at its worst. The pain is waking him up from sleep and preventing him from falling asleep. The pain seems to be worse at night and in the a.m.
He's had a slight fever today and watery eyes.
He did have a tick bite about 6 wks ago. No rash.
Any ideas you can give me would be very much appreciated. Thank you.