You asked similar questions and we went through the low risks of STD by receiving fellatio in at least 3 different threads back in 2005. The answers have not changed: oral sex is safe sex, with low risk for all STDs -- not zero, but much lower than for vaginal or anal sex. As discussed back then, chlamydia is no risk because it is rarely carried in the mouth or throat, so there is nothing to transmit by oral sex. Gonorrhea is possible but uncommon, and not likely to cause infection without noticeable discharge of pus from the penis. Nongonococcal urethritis, perhaps sometimes due to normal oral bacteria, is possible but the risk level is unknown. Syphilis is possible but very rare in most heterosexual populations in the US, including most commercia sex workers -- and would not cause the symptoms you describe. Herpes possible but not common.
Your subtle symptoms, without visible discharge, are not likely to be due to any infection. Vaginal discharge has many non-STD causes, and since her problem apparently is a recurrence of something related to her recent pregnancy and delivery, most likely your extracurricular activities have anything to do with her symptoms. On the other hand, the timing certainly is compatible with the possibility you were infected and transmitted something to her. So to be safe, I suggest that both you and your wife be examined and tested for common STDs. I anticipate you'll both have negative test results.
Since oral sex is generally safe, condoms are not recommended routinely. However, given your anxieties about STDs from oral sex, I suggest you start using condoms when you have such exposures, so you don't repeatedly go through these spasms of anxiety about it.
Regards--- HHH, MD
That's all for this thread.