There was no other activities, so I felt like this was a low risk encounter. But 4 days later I started experiencing a kind of bitter, metallic taste in my mouth. I have no other symptoms of any kind (no rash, discharge, blisters, etc) and didn’t notice anything like that on my partner either. 

Is metallic taste a symptom of any kind of STD?  Should I be concerned here, and if so for what?

This was a low risk exposure. We (or you and Dr. Hook) have discussed the low STI/HIV risks from cunnilingus. I don't recall if analingus was discussed, but it's pretty much the same as cunnilingus:  very low risk for all STIs, if any risk at all for the oral partner. That said, there is controversy about whether oral gonorrhea is common or rare from analingus. The main health risk is for viral diarrhea, various intestinal bacterial infections, certain parasites, and hepatitis A (although the risk for the last two is exceedingly low in industrialized countries).

No STI is a likely cause of altered or abnormal taste. Lasting 4-5 days, I would have to assume this is more psychological than physical. I also wonder if you are taking any new medications, perhaps starting around the time of the sexual exposure. Metallic or other altered taste sensations is a common side effect of many drugs. (If so, you can search online at sites like drugs.com, and others, to find if there is a known association with anything you might be taking.)

To the extent there was any STI risk, it stems primarily from your partner's oral sex on you. Be on the lookout for genital STI symptoms, like discharge, painful urination, or penile sores. I would not recommend STI testing unless something like this shows up in the next couple of weeks. But of course you are welcome to be tested for common STIs if the expected negative results would give you additional reassurance. In that case, you could have urine and a throat swab for gonorrhea at any time (5 days is plenty of time for valid results). (There was no risk for chlamydia, which probably is never transmitted by oral sex, cunnilingus or analingus, but chlamydia testing usually is automatic along with gonorrhea testing.)

I hope these comments are helpful. Let me know if anything isn't clear.

HHH, MD

Given my situation, should I refrain from sexual relations with my girlfriend for a couple weeks, or is that not necessary?

That concludes this thread. Thanks for the thanks:  I'm very glad to have helped. That's why we're here!