I'm losing weight. Is this one of symptoms of herpes.

No really. If you are losing weight, get a complete check up. Unless you have a severe case of systemic herpes, this should not affect your weight, unless you simply are not eating. If your diet and appetite are normal, and you are losing weight, you need evaluation.
Sadly no. I assume you do not mean either cold sores nor having latent herpes because that would include nearly 100% of the population. Genital herpes can cause overall inflammation with headache and fever. But that is really only with the first episode and lasts about a week or less. That isn't enough to cause weight loss.