Yeast is not an STD, so it's a little off topic for th is forum. But I will try to help.
The main thing is to first be certain that yeast in fact explains your current symptoms. It is possible but uncommon for yeast infections not to respond to the treatments you have had, and other things can cause similar symptoms. For example, if your main symptom is burning or itching, you might have idiopathic vulvodynia. If you really have yeast that is resistant to the imidazole drugs (the class that includes all the drugs you mention), there are other treatments that often are effective.
Since you and your doctor(s) seem to be unhappy with one another, a fresh start makes sense. I suggest you seek out a gynecologist who sub-specializes in infectious diseases; such specialists usually can be found in association with major medical centers, especially in urban areas. Among other things, a culture test for yeast (not just looking under the microscope) might be wise, including testing for antibiotic resistance if yeast is actually found.
As to your ancillary questions, yeast does not cause infertility. And while the preventive measures you describe can't hurt, it is not clear they actually work to prevent yeast infectons.
I'm really not really an expert in this area, and it won't help to have an ongoing dialog; this really is a gynecologic problem, not an STD issue. (In my STD clinic, we refer patients with problems like yours to our gyn colleagues.) But I hope this helps get you started on a solution.
Best wishes-- HHH, MD
Tthe antibiotic resistance issue might be quite easy to address with less complexity than I suggested in my reply above. Most genital yeast infections are caused by Candida albicans, which is almost always sensitive to the imidazoles. About 10% of cases are due to Candida glabrata, which usually is resistant to the same drugs. So culturing for yeast and identifying it as C. glabrata may be the next logical step.
C. albicans, glabrata, and sometimes other species are normal inhabitants of the lower intestinal tract, vagina, and/or skin. They are there all the time. Not every woman is colonized all the time, and different species may come and go. But at one time or another, yeasts can be found in the vagina or rectum of most women, with equal frequency in those with and without symptomatic yeast infections. What seem to be new yeast infections usually are not really new at all, but either increased growth of previously present organisms, or a more intense immune reaction to them, or both.
The reasons yeasts sometimes grow to larger numbers, or cause symptoms, remain mostly mysterious. The most common trigger is use of antibiotics, e.g. for a UTI, respiratory infection, or anything else; when protective bacteria are suppressed, yeasts often grow. Poorly controlled diabetes is another potential trigger. But in the vast majority of cases, no obvious trigger can be found. HIV and other immune deficiencies are often cited, but these tend to be overemphasized; it is the rare woman with yeast infections, even when recurrent or severe, who is found to have an underlying health problem of any kind. There is much folklore about tight clothing, diet, exercise, direction of wiping, and so on. There might be something to these risk factors, but mostly that's all they are, folklore. If you think you have identified an obvious trigger that is easy to modify, whether tight jeans or particular foods, by all means avoid it. But don't get your hopes up.
If your symptoms are identical to those you have experienced with previously diagnosed yeast infections, then most likely you are right. Still, don't make that assumption until you have a professional diagnosis. as I said in my original reply. Something else might be the main culprit.
The bottom line is that it is unlikely that there is any underlying health problem you need to worry about. But the final answer about that, as well as about treatment, will come from professional examination, not online research.