Welcome to the forum. Thanks for your question.
Even before I read the question itself, the title alone provides all I need for an accurate opinion and advice. HIV test results always overrule any and all symptoms, exposure history, or any other factor in deciding whether or not someone has HIV -- as long as HIV testing is done sufficiently long after the last possible exposure. And HIV is a far less common cause of a white coated tongue than many (hundreds!) other conditions, including minor viral infections, changes in diet, and others.
Now I have read the rest of the question. First, you had a low risk exposure, since you used a condom. Other details of your exposure like those you mention (how you wiped afterward, for example) never make any significant difference in HIV risk. Second, your symptoms are not at all suggestive of HIV, which would not cause a single localized enlarged lymph node or such brief diarrhea or fever. And as noted above, white tongue is meaningless as a sign of HIV. Finally, any and all existing HIV lab tests are 100% reliable beyond 6-8 weeks, and certainly at 19 weeks. No testing is ever needed at 6 months after exposure.
Those comments answer question 1: You don't have HIV and it is impossible the result would change with future testing. 2) Your weight changes don't mean anything one way or the other. 3) OHL is a sign of advanced HIV (AIDS) and doesn't occur in the first weeks of a new HIV infection; and I've already discussed the coated tongue.
Here is another thread that goes into detail on the window periods associated with various types of HIV test: http://www.medhelp.org/posts/show/1704700
Bottom line: If any symptoms continue that you are concerned about, see a doctor or clinic. But stop worrying about HIV, do not have any more tests, and if you have a regular partner, feel free to continue unprotected sex with that person.
Best wishes-- HHH, MD