Why is my dog wrecking her skin still?

[Claire2009]

I have a labrador, she is two years old. She has had problems with her seasons in the past, instead of twice a year she was 3-4 times a year, followed by a phantom, and this was making her skin very sore under her belly.

She got speyed 4-5mths ago and her skin cleared up, but now she's nibbling herself again, she has a big bald patch at the top of her front leg and is attacking herself in a couple of other places. She has stronghold for fleas and ticks (its the only thing that works for her) and is healthy other than that, so why does she keep doing this?! Could she be allergic to pollen/grass?

She might be.
Or to the food she's on.

One of mine has real allergy problems. I eventually managed to sort out the diet part, after much trial & error, but he still has seasonal allergies.
I give Piriton. The vet ok'd it, in fact even prescribed it at one point but it's cheaper now go buy it at the chemist.
You could try it, see if it stops her nibbling & scratching, then you'll know it's allergy related & can begin the search for the cause.
Not the one a day type, the ordinary Piriton, or chemist's own version of it cheaper.
My little chap who takes it is only a small Yorkie, 7lb weight, so has just a quarter tablet twice a day when he gets bad. Try 1 tablet twice a day. It won't do any harm.
My littlest Yorkie, just 4lb weight, got bitten by a wasp last summer & was going mad with it. I rang the vet & he told me give her 2 full tablets at once, followed by another an hour later, did her no harm but stopped the allergy in it's tracks.