The NHS testing for UTIs is not very good, so you may have one anyway, especially if leukocytes present. Three days of antibiotics is not enough, so hopefully a longer course will help.
You can use both Vagifem and Ovestin, many do. Vagifem internally and Ovestin externally is a good combination as they are two different oestrogens. Three Vagifem a week seems barely adequate to me (I use 5, some folk on here need daily). You could try the Estring, which is equivalent to 5 Vagifem a week. It sounds as though your surgery doesn't know much about VA.
An emollient such as Epaderm or Hydromol, or maybe an oil-based moisturiser such as Yes OB or Olive & Bee, would help protect the vulva from any stinging produced by urination.
If you are not already a member, the private Vaginal Atrophy Facebook support group is a good resource.
I hope you feel better soon.
JP x