can the doctor know that i had sex with somebody ?

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today i went to doctor because i have a Fistel near my anus, and tomorrow i'll have a surgery to remove it but the doctor said that he'll look inside my anus to be sure there isn't any thing wrong there, so the question is: i was bisexual in the past and i had sex with guys, so can the doctor know that i had sex by looking at my anus?
sorry for being rude but really i want to know that because i don't want him to look at me and laugh after i'll wake up from the surgery, and also being gay or bisexual is not regular where i live
thanks for answering and reading.
Only if it was very recent, also many str8 guys stimulate their selves by anal masturbation, even
if it were obvious that there had been some activity in that area, an educated Doctor would think nothing of it.  (+ info)