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So you have been suffering from Bacterial Vaginosis on and off. Also you have extremely dry skin also called " Xerosis " with brittle nails.
Before i recommend you how to prevent it or what needs to be done i need to know a few things.
You said you have been taking antibiotics and even using antibiotics topically. Can you please mention what antibiotics you have taken for the BV till now. And are you on any antibiotic right now? Normally for BV this is recommended,

1) Tab. Metronidazole 400 mg twice daily for 5-7 days
2) Clindamycin gel to be applied locally for the same duration.

So i need to know what antibiotics you have been using till now. This kind of a condition keeps recurring. However it should resolve with a proper course of antibiotic.

Also did you ever undergo any blood test? If you did, kindly upload the reports.
Since you're not sexually active, i will suggest you to completely avoid douching because that also frequently leads to BV.

Coming to your skin problem. You mentioned you have taken Vitamin D before. Did you take it for your dry skin? People with xerosis ( Dry skin ) have further problems such as scaly skin, brittle toe nails, exactly what you are experiencing right now. Are you on any vitamin supplements? Normally dry skin can sometimes be caused due to a deficiency of fat soluble vitamins. So let me know if you're on any vitamin supplement?

Regarding your bloating, some people lack the acid HCL required in the stomach to digest food easily. You might be lacking this acid and hence you get bloated/ suffer from episodes of diarrhoea, after taking bread or pasta. In this case you can avoid dairy products and bread.

So let me know what antibiotics you have used up till now and if you're on any vitamin supplements. Also if you have any reports kindly upload.

Thanks a lot,
Doctor Spring