I am sorry to hear that you woke up in the morning with a thin yellow coating on your tongue and it has you worried that you have have a bacterial infection, or even HIV. I would be happy to give you some information about tongue pathologies and HIV, but ultimately I am going to recommend that you make an appointment to be evaluated by a physician. A good place to start would be your primary care physician
, an alternative would be an ENT (Ear Nose Throat) physician. They will be able to examine you, and take a thorough history and give you a better idea of exactly what is going on. It seems that there are a number of different questions you have. There are many different things that can cause a yellow tongue. Rarely is it due to a bacterial infection. There are certain oral infections that can occur in the setting of an HIV (Human Immunodeficiency Virus) infection. One in particular is oral thrush which can give a whitish/yellowish coating on the tongue that easily scrapes off. the underlying mucosa is usually red and inflamed. This could be one of the signs of an HIV infection, but is no way specific to HIV. Meaning that there are many other reasons for getting thrush that don't involve HIV. If you have concerns about being infected with HIV, then you should get tested, and your primary care physician would be able to take care of that.