I would consider seeing an allergist. In the UK, you may not be able to get max VG as flavorings have PG, but you could get close (or just buy some Pharma grade VG from a chemist or pharmacist, then add VG base nic).
I would probably see a doctor though, itching and bumps aren't good re: allergies as sometimes an allergic reaction can swell dangerously out of control. I have PG "sensitivity" which means that I can't use it, but my symptoms were throat and lung irritation, I wound up getting a "last" pneumonia AFTER I started vaping, but my vaping doc helped me figure it out. Anything more than about 6% PG I really can't vape. I never got a rash or itchy feeling though. And I'd hate to point you in the max VG direction and have you be allergic to VG, and rushed to the nearest hospital for help. If you can get allergy testing done that may help you rule out flavors as well. Probably, (possibly) the allergist may put you on an "allergy elimination" vape diet, but I would really be more comfortable if you did that with a professional, and perhaps with an epi-pen on hand in case you run into troubles (you can get an epi pen prescribed by most allergists) and then you may have to go down the "isolating your vape ingredients" road. Some flavors don't agree with me either. However, I'd say the matter is probably best handled (however you wind up handling it) under the supervision of an allergist.
My kid had allergies and asthma, I got to learn ALL about allergy elimination testing and allergy shots, The good news is after 5 years of allergy shots, the kid no longer had them. Since vaping is so much more of "harm reduction" than tobacco, I'd really say it's worth your time to figure this out, and the good news is, you probably can find a stable vape for yourself, I was able to despite my sensitivity to large quantities of PG. Everyone's just a bit different....
Best of luck, and I hope you can get it sorted out!
Anna