Herpes is the most common cause of genital sores. Although the true initial outbreak always occurs within 3 weeks, some people have asymptomatic infections that ony start to cause visible outbreaks months or years later. From your description, herpes seems unlikely, however. And if that's what you have, you didn't necessarily catch it during the exposure you describe above.
If in doubt, return to your doctor. I won't have any further comments or advice.
Would it be possible for a sore/lesion to appear 163 days after an exposure?
No STD causes the symptoms you describe. In any case, receiving oral sex is low risk for STD. Further, you have seen two providers who reassured you and found no evidence of STD and I agree.
As to other causes of your symptoms, the main thing that enters my mind is the chronic pelvic pain syndrome, which used to be considered a form or prostatitis but might not involve the prostate gland at all. Google "chronic pelvic pain syndrome" for lots of interesting reading; I suggest starting with the Wikipedia article, which is excellent. (It probably will come up no. 5-6 on the google list.)
Good luck-- HHH, MD