OMG i feel the same way! they way you wrote that is like i could have! I am a single guy and live in a remote area, so online is the real only way to meet women, and i am feel the way you do! I have been tested and am good but i still freak out, most of the time a bail before i even meet the girl i'm talking to, tragic i know! I have found that eating healthy and exercise helps a ton! but still mind tweeked!
I'm sorry you're going through such a tough time. The issues that you worry about, especially for someone your age who may be confronting them for the first time, can be overwhelming. That's especially true if you might not have a good support system including people facing the same concerns. I sympathize, because the same or similar issues once caused me to become increasingly worried and preoccupied for a lengthy period.
I don't think you're pananoid or abnormal, and your concerns about your mental health may be related to your preoccupation with your physical health. Most reasonable people would be concerned or worried about these issues. Your responses are understandable given the circumstances, but they don't have to remain constant preoccupations that prevent you from being happy. Reaching out to someone who can discuss them with you and offer advice, as you have done, is a healthy and productive step. You might get the help you need, for example, by participating in group support with others experiencing similar concerns.
If you're not interested in that or don't want to pursue other less formal options, I think psychotherapy with a sympathetic and supportive therapist is a good first step. You may learn that your worries are magnified because of some underlying issue you can identify and resolve. You could process the reasons underlying your worry, or you might learn cognitive techniques for managing them so they bother you less. If for some reason you're strongly opposed to that option, it's not a viable one, it doesn't work, and/or a therpist thinks you have a clinical mental disorder that can't be managed with psychotherapy or other measures, you could consider consulting a psychiatrist about the matter. The symptoms conceivably could be related to anxiety and/or depression. The extent to which they interfere with your life and how long they have done so are important considerations. Given what you have reported, however, I think seeking support in a less formal setting is probably a better way to start.
Meeting people online and by using apps is increasingly common. It certainly may be risky, including but not only because of possible exposure to STDs. Concern about encountering potential predators or imposters who want to victimize vulnerable individuals financially or otherwise is legitimate. You should remain vigilant and alert, proceed slowly and cautiously, and trust your intuition. Worry about HIV is also common and legitimate, especially for those who are in the early stages of confronting the risk. It sounds like you're doing everything you should to protect yourself, and perhaps with time and some support your concern will diminish.
I hope you find the support you need to live the happy life you deserve.
Well, the first thing is a developing phobia. The second is a sign of a rational mind -- online dating is basically meeting complete strangers. Ever try meeting someone in person? But when you get to a pattern of thinking that makes your life harder, seeing a professional therapist is a good first step. Exercise, meditation, all the usual culprits can help. But seriously, the internet is full of nut cases, so knowing that doesn't sound like a thinking problem to me, it sounds like common sense.