Itching of the areas you describe is not an STD symptom, with the possible exception of scabes or pubic lice (crab lice). Scabies is a mite infestation; that and crabs can be sexually transmitted. But scabies causes discrete itchy bumps, not diffuse itching. Herpes doesn't cause the symptoms you describe; even if you had atypical herpes, the symptoms always clear up within 1-2 weeks, never persisting for as long as you have had.
1) If you had been my patient, I would not have recommended testing for herpes based on your symptoms. Technically, you could have caught herpes, since it can take 3 months for the test to become positive. But if so, you have 2 entirely separate problems: asymptomatic herpes plus pubic/scrotal itching of some other cause.
2) No STD is the cause.
3) Speculation only: fungal infection (e.g., tinea cruris--that's jock itch), scabies or crabs (see above), folliculitis, allergic reaction to something--or almost any of the other innumerable things that can cause itching anywhere on the body. You can check yourself for pubic lice by looking carefully for the nits (eggs), which look like little white spots attached near the base of pubic hairs; or for the lice themselves, which first look like little brown spots (the size of a pin head).
4) If you see nits or lice, over-the-counter treatments are avilable. Also, it wouldn't do any harm to try an over-the-counter cream for jock itch. Otherwise, your only option is to see a health care provider.
5) I don't think I ever said herpes is hard to catch. It's actually pretty easy. Anyway, lots of things other than ease of transmission contribute to the prevalence of an STD in the population. But it's clearly not an issue in your case.
Good luck--- HHH, MD