How long till antihistamines kick in dunno

so i’ve been dealing with these hives and flushing for a bit now, and my doc put me on some antihistamines. i’m kinda lost on how they work, though. how long does it usually take for them to start working?

i’ve been taking them for a few days, but i’m still getting these random flare ups… is that normal? should i be giving it more time or is there something else i should be looking into?

fwiw, i’ve been tracking my symptoms and it seems like heat and certain foods are making it worse. any input would be helpful, thanks