If I donate blood, would they tell me if I have an STD?

Is it required for organizations like United Way to inform you if your donated blood is not usable due to illness such as an STD? I have donated with them twice and have not received any notification that I have/had anything, but I'm thinking that there may be a possibility that I might have herpes (and did at the time of donation). Not only did they not notify me of such, but they also called me as a registered donor asking me to donate again. Is this something they test the blood for (or CAN IT even be tested for via blood), and would they notify me if my donation was unusable due to something like that?