No I meant how does it build up there? As in the mechanism. I can just google it though.
Was this your only exposure to k9 semen?
You don't generally go from no reaction to anaphylaxis after several exposures. Primary immune response will usually be rather mild, then a secondary response will be fantastically worse.
I had a mild reaction on my second dose of doxycycline after a tick bite. Thought it was the tick bite. Took another dose that evening, and within 10 minutes felt the vacuoles forming. It's iterally the only thing I'm allergic to, and I had a secondary immune response on my third exposure. Took benadryl, was fine, but you want to be very careful. Make sure someone is expecting you to report back and can secure you before EMTs arrive... since they'll probably do a vaginal swab if you're unconscious and have a large puddle of semen between your legs, and no male human around...
But if this was more than your third or fourth exposure, I would ask a few more questions to eliminate things like a flea treatment (often ivermectin, etc) or a recent vaccination.
If benadryl wormed, but you then coughed up clear fluid, you likely had absorbed enough semen degradation products (or whatever you were allergic to) to produce antibodies, and those were still circulating, and when the benadryl wore off, you had a continuing histamine reaction to the still-being-absorbed semen/products/latent compound.
A little more information would go a long way DM if you don't want to post it here, but I might be a biologist or something. ?