My 17 Year Old Son Was Seen At The Dr

My 17 year old son was seen at the dr 2 days ago for frequent (>than 10/day) hard bloody stools. they ran blood tests (all fine) and diagnosed constipation. He is taking Colase and his symptoms are improving. Now tonight he is running a fever, has a severe headache and achiness. While these are flu-like symptoms, how likely are they to be connected and should I be worried?