Herpes and shingles are actually caused by two different viruses, from the same family. What we traditionally call "herpes" is caused by herpes simplex. Oral herpes, causing fever blisters and cold sores, is called herpes simplex 1. Genital herpes is caused by herpes simplex 2. The condition we call shingles is caused by herpes zoster. Herpes zoster is the same viral infection that causes chicken pox, and the herpes zoster virus can live in the body for years after the case of chicken pox is gone, and re-emerge as the painful blisters of shingles.
The same medication can be used to treat both infections, but a higher dose is used when treating shingles.
Note that the blisters on your arms and legs may not actually be related to herpes at all. You should see your physician for an evaluation.