My Son Is 5. He Was Complaining About His Knee

My son is 5. He was complaining about his knee hurting yesterday. When he got home from school he had a fever of 101. Today he's had a fever of 99 that with Tylenol and 101.5 without. My sister pulled a tick off him earlier and I pulled one out of his hair tonight. He's complaining his neck hurts tonight and still running a fever.