There are so many different diseases that cause rash along the body, not just syphilis. This infection can be transmitted even when condom is used, if your skin touches the chancroide, but as you said, you didn't see any signal on that lady's skin, which probably indicates the lack of that std in particular. Sometimes, chancroides can be inside the body, but that wouldn't have exposed you to syphilis, as you were using condom. Oral sex would have exposed you to syphilis though, and also to gonorrhea and herpes.
As it's been already 7 weeks, if you test for gonorrhea, your result will be accurate, and a test for syphilis could be accurate as well, but there are people that take longer to show a positive result, so it would be better t wait until it's been 3 months since you had the intercourse. For herpes, the window period is also 3 months.
Honestly, I think you are worrying too much. The risk is really low. Go to get your test, but I am sure you will get a negative result.
All the best.