Hi , I'm James DVM MRCVS and would like to help you with your question
Sorry to hear about Pip's itchy belly
by the sound of it your vet is right , she might be allergic to something she is coming in contact with , especially something she passes over on her walk (say - cut grass , some specific shrubs)
It could be as well something she lays on . You might be using a new detergent in your wash which she might come in contact with and may result in her presenting symptoms
What I can suggest is the following :
a. try and avoid the causing factor whenever possibly (I know at times it's close to impossible)
b. use Piriton (of the counter drug) at a dose of 4mg up to three times a day (every 8 hours) - this is an antihistamine which works very good on allergies.
There are other drugs which you vet can give you - some contain steroids and some other substances which are stronger but I rather you give piriton a try first .
I hope this helps .
if you have any more questions - please let me know
all the best
well - creams that contain alovera are always good as they themselves contain soothing elements . even sudocrem is a good substance but all are for after the effect only and will not prevent it . while Piriton will help reduce the symptoms and much faster and more efficient