As your doctor told you, this is an anxiety/brain issue, not an HIV issue. It's not uncommon for people to experience severe anxiety after a sexual encounter they feel guilty, regretful, and shameful about, especially if that person is in a committed relationship. That fear presents itself as worry over contracting an STD, like HIV.
You need to continue working with your mental health provider, preferably a therapist, who can help you change the way you think about HIV.
Thank you mam...sorry for rather late reply. Mam the problem with me is that i keep on thinking is that if test was not done right. If there is a small ulcer in my mouth i think of it as HIV issue. Even though my test prove to be negative. Every time i try to live a normal life with my wife. Some ulcer or some sore throat stops me. It is very difficult for me to get over this. Please suggest