Some are reluctant to go to their doctor on something like this, if they even have a doctor. In the U.S., you might want to talk to a local Planned Parenthood clinic. Where I live, these clinics do a big business in STDs, much of which isn’t related to conception, etc., at all. Even gay men go there for these problems. It helps the clinics pay the bills.
If you think you may have been exposed, you can be tested for something like gonorrhea. But, these tests are not always completely reliable. So they generally prefer to just go ahead and treat you for gonorrhea and chlamydia, each of which involves a single-dose med, if they think it’s likely that you’ve been exposed to either. In fact, if you just tell them that you’ve been notified that a recent sexual partner has tested positive for gonorrhea, they will probably just treat you for both STDs and not bother with the tests. (That may vary in different states.)
You can usually get in to see them within a few days, and there’s nothing you can tell them that they haven’t heard many times before. The cost depends on your income, but the whole thing, including the meds, should be less than $200 if there are no tests done. You can even make up a fictional identity if you want, including SS number, but one or more of the meds they give you may be by prescription, which you’ll have to get filled somewhere else using that name and SS number.
But that still doesn’t cover syphilis or HIV, which you should ask them about. If there is no active lesion, then blood tests are used, but you have to make sure enough time has passed for the antibodies to show up. For HIV, most people will convert within 6 weeks, but some take longer. Three months is generally considered to cover virtually everybody. I don’t remember what it is for syphilis.
I hate wearing condoms, but you know, if you don’t use them at least for vaginal and anal sex with multiple partners, you’re just going to go through life constantly facing these problems, and potentially infecting others.