How are you able to tell?
By looking at it in the photo, of course. From the way it looks, my first guess would definitely be oral thrush for the simple reason that this is the most common cause of a yellowish coating on the tongue, which the photo clearly shows.
To be even more certain, I would ask you; have you experienced any other symptoms whatsoever?
Second, I would ask you to test my guess by going on a Candida diet for seven days paying very close attention to the reactions you experience each day. At the end of seven days, you should know for certain whether or not you have oral thrush, or — you can find a doctor and spend your money to have him tell you that there is no such thing as a Candida infestation.
I had an potential exposure to HIV and even though I tested negative 12 weeks after, I am very scard. I have too many other symptoms…