Thanks for posting your query,
An ulcer on the penis foreskin is not necessarily due to an STD
but could be due to another type of infection that has complicated into an ulcer. Just the act of penetration (with friction on the vagina) can cause a small lesion which could easily become infected and later on complicate into an ulcer. It will be recommended that despite your convictions that you do not have an STD, you should go in for screening of all STDs (syphilis
, chlamydia, herpes
etc). You should continue both treatments and you may require additional oral antibiotics
and maybe local antibiotics such as neomycine cream. Also get your partner screened.
Hope this helps