Experiencing fatigue,fever and abdominal pain

Hi! My boyfriend started feeling really bad last night. He is 21 years old. We live in Charlotte, NC. And he is experiencing fatigue, fever, abdominal pain (more on left), and frequent and painful bowel movements. Yesterday we went hiking and swimming at Stone Mtn, NC. When we got home at 11:00 pm he began complaining about his joints hurting. He said it felt like his elbows and knees were burning and that his back was sun burnt. Well, he was not sun burnt and he shouldn't have been weak from the hike because we barely did 3 miles and we usually do 10 or more and he is very athletic and fit. He also was having very frequent and painful bowel movements but not really diarrhea. He was also having lower abdominal cramps more on the left side than the right. He started having chills with a low grade fever which just got worse through the night. This morning he said his whole body ached and his fever is now 101. His head is also hurting. He went to get something to drink from our kitchen downstairs and I found him laying on the steps because he got tired on the way there. This is very unusual for him, we have been dating for 5 years and he has only been sick once. Thank you for your help. P.S. I thought he may have gotten a tick on him from the hike, but there was no tick on him this morning.