Well, if you have tested for std's and have been negative, then it is not std. If not, then you need to test. As I stated above tickling is a general symptom that can indicate many things. Some things may not be std related. With only that information and no way to test or examine you, there really isn't anything we can advise you on.
i do unprotected sex and oral sex,only with my 3 years relationship. I've done all the tests and the doctors don't find anything. No psysical problem in the urethra, i have no anxiety, no stress nothing psycological just that sensation of tickling which doesn't go away.
That is a general symptom. Did you have unprotected sex recently? You should maybe seek another opinion and/or have testing done to pinpoint the cause.