I think D-mannose helps when their is a certain bacteria in the urine. I once emailed the company who makes it and they told me they did not think it would work for me. For me all my issues were VA related.
With VA there are times it does flare. It can even flare from stress. I have found switching from baths to showers helpful. I also only wash with emollient. I apply some to the vulva, wash it off in the shower then reapply to act as a barrier. This was advice given to me by a menopause DR. She told me I was making myself more dry by washing with water alone and she was so right.
Like you, I cannot afford to go private so I think the best thing may be to try to talk to the practice manager. If they knew their GPs were so uneducated in menopause then it would help. VA can feel like a UTI especially during a flare.
There is no harm in asking for a urine sample to be sent off if it will put your mind at rest. I would do it as soon as possible as you are worried.
They close the econsulats at 6.30AM! Who on earth is up that early! Not me.

Perhaps you need to be frim with the reception and insist you need an appointment. Not easy, I know.