I'm immunosuppressed and frequently get oral thrush. i'm on day 5 of my second 14-day round of fluconazole, and not getting any relief. is it possible that i've become resistant? is it wise to try something different at this point?

Yes, resistance is likely. Up to 10% of Candida species causing localized infections (thrush) are C. glabrata, not C. albicans; and C glab is resistant to the azole drugs like fluconazole. Other species also may be resistant, and this problem is especially common in people with repeated or recurrent candida infections. Discuss with your doctor; ideally an infectious disease consultant. Good luck.