I concur, be very careful.

I can get hives that spread but usually I can tell where they started. Sometimes it's shoes (boots rubbing on my calf), sometimes it's where the clothes touch my body like waistbands and underwear. If you scratch, they get worse and spread.

I had an all-over reaction once and that was a reaction to an antibiotic. The hives took a long time to go away and even after they started fading, I still got sick really easily. I'd say it took over a week to feel ok internally, if that makes sense.

Hydrocortisone helps a LOT (have it in bulk at Costco) as does Benedryl. There is a Benedryl specifically for hives now. My doctor says also to make sure that the affected areas don't get too dry - I've found that the skin affected gets really dry and just has a different feel to it.

Definitely see the allergist but maybe you could journal too? Like write everything you eat, do, wear...even the laundry detergent you use. Maybe you can find something that is a common thread. Maybe you have stress before an athletic event and that is a contributing factor? I know it can be with me...I'll have these "I can't get sick, I can't get sick, I can't get sick" events and because I'm so stressed about not getting sick, I get sick

Good luck and be careful. If you have doubts about how you feel before the duathalon, err on the side of caution. Your body is still recovering beyond just what's on your skin.