Dear Dr. Wes & Katie: I just found out from my yearly pap smear that I have a yeast infection, bacterial vaginosis and chlamydia. I have zero symptoms for any of these. At least I tested negative for herpes. How in the world does this happen? Can I get chlamydia without my boyfriend having cheated?

Wes: You raise a lot of issues in a very short question, which rather poignantly underscores why sex is just a little more complicated than many teens and young adults would like to believe.

Of course these three problems don’t really fit into the same box. Vaginosis may be associated with sexual activity, particularly as you encounter new partners, and that’s been my clinical experience, but the CDC notes that nonsexually active women can also contract it. According to the Mayo Clinic, yeast infections are even more common and can be carried back and forth with sexual contact. But neither of these conditions are considered STIs.

Chlamydia is the second-most-common sexually transmitted infection after HPV (human papillomavirus), and young people 15 to 24 are at greatest risk of getting it, accounting for half the 10 million annual infections. The most frustrating thing about chlamydia is that in 70 percent of cases, it’s asymptomatic but still present and dangerous. So you’re in an unfortunate majority.

The CDC and common sense suggest that if one is sexually active, he or she must without question be tested every year for the full range of STIs, and in between partners.

Now, I work with young people and am all too familiar with their tendency to randomly hook up these days. So I’m aware that VERY FEW actually get tested until they start getting worried. And that’s why we have such a high rate of infection.

The fact that we can usually cure most STIs seems to have actually lowered people’s vigilance, preferring to just deal with things as they arise. This is a terrible idea with chlamydia since it can quietly spread to the uterus and fallopian tubes causing pelvic inflammatory disease, permanent damage to a woman’s reproductive tract, infertility, long-term pelvic pain and ectopic pregnancy. That’s a really high price for avoiding good advice

Thankfully you don’t have herpes, which I should remind readers can only be treated and cannot be cured. While the rate of infection for HSV-2 is “only” about 776,000 annually, those cases accumulate year after year, so that 16 percent of Americans age 14 to 49 now have it.

As for your boyfriend’s fidelity, it’s hard to know based on this data. Because of the whole asymptomatic thing, we can’t know if the chlamydia came from his previous partners or a recent, secret one. And unless he’s your first (or you got tested before you two started dating), you could have contracted the STI before meeting and given it to him.

I understand that’s frustrating, but making any decisions about a relationship based on what you’ve shared is dicey at best.

Good job being responsible and getting tested. I hope others will learn from your example this week. In the meantime, talk to a specialist about how to adjust your natural biology to reduce the chances of vaginosis and yeast infection.

Katie: Many people will at some point undergo the unfortunate experience of acquiring a sexually transmitted or other type of vaginal infection. Having three different infections at once would certainly make for a glum few weeks. Luckily, as long as you’re treated immediately, all these infections should clear up.

As a teenager with no intention of going to medical school, I’m not qualified to give input into the causes and treatments of these infections.

Regarding your boyfriend, however, I’d encourage you to follow the principle of “innocent until proven guilty” as you work to uncover the source of the chlamydia. In a long-standing relationship, a sexually transmitted infection might be more likely to result from cheating. But speculating about that likelihood won’t solve the problem.

The easiest way to unravel the chain of infection is simply to talk about it with your boyfriend. Even if you don’t suspect him of cheating, he’ll need treatment as well, and you both have a responsibility to alert sexual partners from the recent past that they may also be infected.

You might find the point of origination somewhere in those contacts, but you’ll get a quicker answer directly from your boyfriend.

The seriousness of an STI should encourage him to answer honestly.