Welcome to HCM
We understand your concerns
I went through your description. I suggest you not to worry much. You could be correct. You are becoming paranoid because of your guilty feeling. The remedy to it is understanding the pathology and body chemistry. You do not have any symptoms of STDs, as you have already mentioned. I don't think evacuation habit has anything to do with STDs. That is a habit. You change any habit just by your will. You do not have to worry about STDs.
Regarding your HIV
scare, you have to be logic. If you want to be confirmed, you should get it tested. There is no other alternatives. Worrying and being anxious cannot treat your HIV. Correct? Stop worrying and be logical and accept it as it is.
Hope this answers your query. Available for further clarifications.