Because different practitioners have access to different products as well as products in the private sector mayB pricer than the NHS is prepared to have in the pharmacy.
Whilst ABs will ease symptoms of vaginal atrophy/urine infection feelings they cannot replace oestrogen lost. They are after all an anti-inflammatory. Why has your GP surgery not rung you to explain whether is/not infection present in the sample? 3 days often isn't enough of an AB even 1 that is prescribed for a specific bug.
Continue with the Macrobid . Your surgery may not be pleased if you went privately without being referred ..........

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Let us know how you get on. And continue with the VA treatment every night for at least 3 weeks along with pain relief if necessary.