Illness after hard race efforts

Over the last year I’ve repeatedly experienced illness after short intense race efforts. Any CX or XC race under approximately 90 minutes seems to cause this. This coincides with me getting relatively faster on the bike from structured training, and also discovering that I can cross over a pain threshold that I used to back off from.

It always follows the same pattern with lots of coughing as I lay down that evening. Then the next couple days I experience aches, chills and perhaps a fever. The strange thing is that it’s intermittent, and I’ll feel fine for an hour then feel lousy for a couple hours.

Does anyone else have this happen, and been able to diagnose exactly what’s going on?

I’ve talked about it with my physician and pulmonary doctor, and they haven’t really offered any explanations. I think my dr said it’s probably a virus.

I do have exercise induced and regular asthma, but other than the coughing fits I think there’s something else going on. It sucks because it makes me reluctant to race hard because I know I’ll pay the price for most of the following week.