Increased frequency of sex is often associated with bacterial urinary tract infection (UTI) in women (i.e. bladder infection = cystitis); the term "honeymoon cystitis" used to be commonly used to describe it. The most common cause is E. coli, but different strains than associated with food-borne diarrhea. It isn't acquired from the partner, i.e. not an STD, but is common in and around the vagina. Sex massages the bacteria into the urethra.
So your use of "cystitis medicine" may have been appropriate. Then perhaps you got a yeast infection, which can follow antibiotic therapy. (What extra antibiotic did you have lying around?)
Having said all that, depending on the extent of secretion exchange on hands or through genital apposition (without penetration), your symptoms could be due to a vaginal infection other than yeast, such as trichomonas; or to chlamydia, gonorrhea, or herpes. Most likely not, but if your symptoms persist, you will need to see a health care provider.
Best wishes-- HHH, MD