Hi there,
Just typed up a long reply on my phone and the bloody thing crashed on me... arghhh!
I had Chronic Idiopathic Urticaria about 8 years ago for nearly a year. Started in the February and after a couple of months back and forth to the GPs with no cure, was initially referred to an allergy specialist who I saw in the May. Not very helpful at all (had an appalling bedside manner) - had been on Fexofenodine and Ranitadine from the GP already, but took me off those and tried me on Hydroxyzine which knocked me completely out even when starting on a low dose as recommended by my GP and insisted that I take Cetirizine despite me saying that I'd tried it before for hayfever and it gave me a headache (apparently I should just lump it). He then proceeded with allergy tests even after I'd had to go back on Prednisolone the morning of the tests due to angioedema and full body hives breaking out when I tried to stop the antihistamines for 72 hours in advance of the tests (if I was being cynical I'd say he knew that the tests were fruitless at that point but was going to charge for them anyway...) - we had full on blue light ambulance outside our house at 5am after we called NHS 111 in the middle of the night because I could feel my throat swelling up.
After that, I was on Prednisolone for a couple of weeks to bring the hives and angioedema back under control and then back on the original antihistamines. Feeling thoroughly disillusioned with the original consultant, my DH did some investigating and found Prof Malcolm Greaves at the London Allergy Clinic, who I saw in July/August and I cannot recommend him highly enough. He put me on off-label dosage of Fexofenadine 180 - 3 tablets per day. And he told me that I needed to experiment with when to stagger the doses to provide the maximum relief (i.e. I didn't have to spread them out evenly). I was also on Ranitidine.
I also tested positive for pressure hives (knicker and sock elastic was really bad). We think (although can't prove) that my hives were trigged by artificial food colourings and then hayfever season arrived, by which point my immune system got itself into overdrive and started attacking itself. The antihistamines did bring it under control, and I think I was down to 2 Fexofenadine by the October and off them completely in the January. Touch wood I've not had a breakout of hives since then but I am rigorous about avoiding artificial colours in everything, including pharmaceuticals, which is a complete pain in the arse - seriously, even some anti-histamines have colours in that have been linked to hives (the Hydroxyzine I had at the time did, and recently discovered that Dr Reddy's brand of Fexofenadine 180 does too - which I don't understand because none of the others do, they're all coloured with just iron oxide)
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I still take Fexofenadine and Monteleukast for hayfever season (and I'm still on the 180 not 120 dose). One thing I didn't realise until about 3 years ago though is that you shouldn't consume grapefruit juice with Fexofenadine as it stops it working - I've yet to find an instruction leaflet in any of the packs that actually says that - which is ridiculous! Guess what fruit juice I used to have with my breakfast...?
Ranitidine is a good extra one to take as someone else above mentions, it's a different receptor, H2, compared to the other antihistamines which work on the H1 receptors (there are two other histamine receptors, H3 & H4 but no drugs as yet which work on those), so may well help if the Fexofenadine isn't currently controlling it completely. I don't think I started taking Monteleukast until after the hives, as part of my hayfever treatment (I now get seasonal asthma which affects me when I exercise hard outside in the hayfever season), Monteleukast works on the leukotriene receptors in the lungs and bronchial passages so may or may not help with the reaction you're having.
Sorry, that was a bit of an epic post! It was something that affected my quality of life pretty badly (and at the time didn't know when it was going to end) that I'm quite passionate about it still.
Happy to answer any other questions.