Had general testing for stds. They didn't test for hsv2 even when I asked for the blood test, said they only test if theres sores. How come?

See a dermatologist. You certainly can get this blood test. Many are infected without knowing it. Transmission of the virus to others may occur in the absence of blisters. Most infections of hsv2 occur from contact in absence of any symptoms. Cultures reveal presence of herpes virus between attacks, even from infected people who have never had a typical lesion. Atypical symptoms are the norm.
Why should they? The herpes simplex bloodwork still isn't super-accurate. If you've never had sores, and you got a false-positive result, we'd be doing you a real disservice. You can't transmit it without sores, and don't want to be treated without sores. As a pathologist / lab specialist, i'm always explaining the limits of what we do. Thanks for understanding.