Anybody can say anything they want on the internet. I'm confident you didn't find any professional sites saying amoxicillin is reliable against these STDs. It would prevent some but not all these infections.
But it sounds like your partner probably is at low risk for STDs in general.STDs become quite uncommon in women beyond age 25. For example, routine chlamydia testing is not recommended in women older than 25; too few are infected to make it worthwhile. As I said above, I would not have recommended testing for any STD. However, the amoxicicllin will further reduce whatever low risk there was, e.g. for gonorrhea. You don't need STD testing and shouldn't be worried about infecting anyone else.
I will also add that this contact was 4 days ago
The amoxicillin was prescribed for a sinus infection. I have read that this medication can abort the incubation of these sti's. My partner was a 31 year old female. I have had experiences with her before with no issue but it has been over a year. I was wondering if I need to worry about spreading something to someone else or if I was stressed over nothing.
Welcome to the forum.
Was amoxicillin prescribed as STD protection on account of your oral sex exposure? Or you were given it for some other reason? If the first, the prescriber obviously is not an STD expert.
Amoxicillin is not recommended to treat or prevent any STD. It probably would prevent syphilis, but oral sex carries virtually no risk for it, especially from a female parnter. Chlamydia is virtually never transmitted by oral sex, but even if it were, amoxicicllin is not reliably effective. There may have been risk for gonorrhea, but amoxicillin is not active against about half of all gonorrhea strains.
The risk of any STD from a single episode of oral sex is very low -- higher with some partners than others, but always low, and I would not have prescribed any antibiotic at all. If you'd like to tell me more about your partner, I may be able to help judge the risk. In the meantime, unless you have another reason for amoxicillin, I suggest you stop taking it.
Best regards-- HHH, MD