Your risk for developing and STD from oral sex is quite low. The diseases you can be checked for are:
The first three do not have symptoms (usually) early in the disease but should be positive within 1-3 months.
Herpes is extremely common and can be checked by a blood test but may not be from that experience (could even get it sharing drinking glasses with someone)
If she had gonorrhea or herpes in her mouth, she may have passed these to you. Chlamydia does not usually get passed to the man with oral sex.
Saliva does carry HIV and hepatitis C (in low levels). They are spread by sharing blood (dirty needles, transfusions, anal sex, etc) As long as there were no open sores on your penis and/or there was no blood involved (sores in her mouth) the likelihood of transmission is low.
As for gonorrhea, chlamydia and other less common conditions, as long as you don't have any discharge or sores on your penis, or burning with urination, the chances you contracted them is almost zero. The chances of having a positive test on these from receiving oral sex is low.
If you were tested for HIV, Syphilis and HCV at one month and at six months and both times they were negative, you are in the clear.
Any follow up questions are at no additional charge, even after you "accept" my answer.