Thank you for asking. the boring sensation just after sex, could be an indication of irritation to the urethra that could have occurred while intercourse or oral sex. If there is an associated symptoms of pain, discharge through the penile opening, redness, rash at the opening, etc there is need to be getting investigated for urinary tract infection due to STDs. Since you have tested negative for
STD, there is less risk. However, You must repeat the testing after 10 days once more. Also. I would advise you to get a Urine Microscopic Examination and testing done. It can reveal more findings if any.
Next Steps
Drink plenty of fluids and water. Get the above mentioned investigation done.
Health Tips
Don't worry. There is nothing serious.