Reacting
firstFirst progesterone mc10
First progesterone mc5
First-progesterone vgs 100
First-progesterone vgs 200
First-progesterone vgs 25
First-progesterone vgs 400
First-progesterone vgs 50
First-testosterone
First-testosterone mc only to the title you chose for your question, before reading anything else: STDs rarely cause rash in that location. Most likely something else is responsible.
TineaAthlete's foot
Athlete's foot, tinea pedis
Dermatitis, reaction to tinea
Folliculitis
Jock itch
Ringworm
Ringworm, tinea capitis - close-up
Ringworm, tinea corporis on an infant's leg
Ringworm, tinea corporis on the leg
Ringworm, tinea manuum on the finger
Ringworm, tinea on the hand and leg cruris (
jockJock itch itch) probably is a good bet.
Now I have read it. Receiving oral sex is low risk for STDs in general, and could not plausibly result in an STD with symptoms in areas not directly contacted during oral sex. Almost certainly the oral sex is not the cause of either the rash or your anal irritation. Had you been my patient, it would not have entered my mind to test for herpes, unless the rash was highly typical for that STD. As for the questions themselves:
1) Nope. See above.
2) You aren't missing anything from an STD standpoint.
3) Hemorrhoids per se would not cause a rash. However, any number of things in addition to hemorrhoids cause anal itchiness and irritation, including anal fissures, minor infections of various types, and simple pruritus ani. The last is the "wastebasket" term for anal irritation that isn't otherwise explained, maybe sometimes due to hygiene. (The name just means itchy anus in Latin - sort of like saying someone has pyrexia rather than fever.) Or maybe you have 2 problems, the anal itch and the rash behind the scrotum, for which jock itch still seems a good bet.
4) Ideally, you should see a health care provider before trying to treat it yourself. However, you could safely try an over-the-counter cream intended for jock itch, such as Lamisil. Look in the pharmacy along with the athletes foot products. If that doesn't result is substantial improvement after 3-4 days, definitely see a health care provider. In the meantime, don't worry about herpes or any other STD as the explanation.
I hope this helps. Good luck-- HHH, MD