Mutual masturbation is an abnormal way to get any STD. The only realistic case would be touching a chancre and getting syphilis. You said you were fingering that lady, and then you touched your penis. If her vaginal fluid got inside your urethra there was a theoretical risk of gonorrhea, chlamydia and herpes, but risks are negligible.
You can test as follows:
-3 weeks after the exposure, for gonorrhea and chlamydia.
-6 weeks after the exposure, for syphilis.
-3 months after the exposure, for herpes.
All the best.
There is no risk from this.
Here are some posts from our experts (when we had them) that may help -
- read this thread thoroughly. There is an excellent explanation about why certain activities are not risks, and why others are.
I expect all your tests to be negative based on what you describe. Make sure you are drinking plenty of water, lay off the alcohol and caffeine if you drink a lot of either or both, and if your symptoms linger, follow up with your doctor.