Your GP shouldnt prescribe antibiotics unless there is evidence of an infection. There is a lot of guidance now on not giving out ABs as they increase resistance. If you have an inflamed vulva, due to loss of estrogen, ABs aren't going to do anything.
If you have thrush, they will make it worse.
It's common (but not nice) to have some soreness when using vaginal estrogen and this takes time to wear off, once your skin thickens. It's a slow process where the skin changes back to its normal healthy self.
The best thing to do, in all honesty, is to use a tiny amount of Ovestin cream and persevere. Yes, it does sting but it should soon improve.
Vagifem is stronger which is perhaps why it made you so sore.
There are also several other types of vaginal creams etc that are even weaker than Ovestin. One is called Gynest (and it 10 times weaker) and the other is Blissell gel. Both are worth trying.
If your GP isn't familiar with this, can you see a different dr?