pussy problem

I am a 19 year old female and I think I may have picked something up. My vaginal discharge has been much heavier than usual. It's as thick as a bad yeast infection, but yellow like lemon yogurt. It doesn't itch much, only if I don't change my panties at least once during the day. The odor is the real problem. It's a sharp, fishy odor. I have to wash my panties as soon as I take them off or my entire laundry hamper stinks. I tried treating it with yeast infection medicine, but that didn't work. I know I need to go to the STD clinic, but I'm embarassed. What should I expect?