First, if you had HIV exposure, do you have AIDS? Or do you mean your feared but untrue HIV exposure? It appears you don't have HIV, so it appears if you had any exposure your immune system worked fine and you're fine. But that doesn't mean you don't have some other problem, and the fact you saw a GP doesn't mean all that much, they don't check for all that much. A lot of what you're describing are usually gotten by taking certain medications, especially dry mouth. Are you on any? So yes, this can be psychological, which would assume you're thinking like an anxious or depressed person, which you would know because you'd be having chronic anxious or depressed thoughts. Nobody here can tell you if you have a physiological problem or a psychological one. We don't know how you think and we don't know how thorough your medical exams were or if you were sent to a specialist or not. There are things we can have that are very hard to find, such as thyroid problems, nutritional deficiencies, blood sugar problems, hidden viruses or infections, etc. that are hard even for the best doctors to find. So anything is possible. Whether that is likely or not is beyond what you've said so far. What we can tell you is, you can't diagnose yourself on Google. The same symptoms can be had from many different causes. The best we can say is, you've been seen by three medical professionals and told you're fine. But you don't feel fine, and they might be wrong. But when 3 professionals tell you you're fine, assuming they looked for everything possible to look for and not just for the HIV you are most concerned about, it is time to look at your mental state and see if it's so stressed you might be making yourself ill.
I read your previous posts in the HIV forum. You tested conclusively negative and you do NOT have HIV, and it is time to forget about HIV and focus on finding the real cause of your ailments. Continuing to focus on HIV when that is one disease that has been ruled out is not healthy for your mind, and it is preventing you from getting to the true reason for your symptoms - whether they are psychological or physical.