it seems you have some injury
while entery. do you. have anal sex also? this is found many times in such couples. if so many doctors have seen, you surely have no STD
. I would suggest to use KY Jelly when entering and observe adequate hygiene. this type of lesion can come if female partner is either very apprehensive ,or too much force is used, or when time taken for discharge is a bit too long.
you can further send enquiry .i can help you out of this problem
Dr Saatiish Jhuntrraa