Realistically no. 6 years with no symptoms is highly unlikely. If you have not slept with anyone else it logically comes down to 2 variables.
1) You do not have an STI (From your symptoms it is this. Chlamydia and gono do not just show an increase in urination.)
2) You need to have a chat with your partner and he may not be telling the truth.
I believe it is option 1 but I think taking a test could be a good shout if anxiety is there. It is possible that woman get NSU (its harder to tell) which would not be positive on a UTI test but it does show white blood cells.
The test for both of those infections would be a urethra swab. If that was done at least 6 days after exposure then you dont have either. Normally with these std,s there is also a white puss urethra discharge and burning and itching when urinating.
Well, options are:
1.Vaginal swab for gono,chlam,mico/ureaplasma and another urine analysis preferably firsth void urine, to search for chlam/gono or mycoplasma.
Have a heart to heart with your boyfriend. Chlam can be silent for years depending on your immune system, though those a re rare cases.