This sounds like something serious. See a different doctor. Tell him/her as much as possible. Ask to be referred to a gynacologist for a look. Some of your symptoms sound famiiliar with cysts on the overies. It might not be that, but it might be something else equally or more so serious.
Your luck with docs and nurses sound bad. Back/side pain is common with kidney problems, alongside UTI's, but I used to have kidney problems and the rest of your symptoms don't sound likely to be connected with kidney infection.
Thrush symptoms are quite different, and I'd honestly be suprised if it were an STI causing these symptoms, but that doesn't mean don't get checked. I get regular check ups even if I'm sure I'm clean. I like to think it makes the statistics look better. ;-)
I'm no doctor, but have friends who have ovary problems and it is possible there is something wrong there.
Get a better doctor. Even if it means travelling to a hospital. Ask your practise for info on traveling expenses and ambulance taxis in your area as you may get travel for free if you need the appointment.
Don't be alarmed if they test you for everything up to and including cancer. This means they are ruling the most serious stuff out first and means they are doing their job properly.
Good luck, hope you find the root of your problems soon and I am wishing you the best.
*Big Hugs* xxx