An antihistamine would help. I've also been told to put a spoon in a hot drink for a bit and let the spoon warm up then place the back of the warm spoon on the bite and it takes away the itching 😀
You have to get the thailand pass no matter what. Test and go will be available from the 1st Feb and also there's the sand box scheme that's available now. I think you're getting the thailand pass mixed up with thinking it's the test and go scheme which you can't apply for untill the 1st Feb.