I had sex with someone who i had oral herpes and after she kiss my neck 4 days later i have an itch on my neck is that a sign of an infection?

Yes: The herpes virus is transmitted by contact and bodily fluids. It is known that mothers transmit the herpes virus to their children when they kiss them. The sore would have to betin as a red, blistered area which is filled with fluid which contains the live virus. An itch on your neck could be from the oral herpes virus. The period lasts 7-10 days..... Do not touch it with your hands.

Perhaps: It could be herpes, a contact allergy to her makeup, a mechanical irritation to the skin either related to sex or anything that happened to your neck before or afterwards. See a dermatologist for diagnosis. Herpes simplex virus usually requires a break in the skin to cause an infection in the skin.

Possible, unlikely: The herpes virus that causes oral herpes is (usually) different from the one that causes genital herpes. It is the cold sore virus. This is usually transmitted via saliva and unless the skin on your neck was broken (eg shaving rash) it would be unlikely to infect the skin on your neck and not your lips (presuming you also kissed). https://www.dermnetnz.org/topics/herpes-simplex/

Probably not: Oral herpes generally causes mouth blister painful rather than itchy rash. Herpes infection can rarely complicate dermatitis but this is quite painful. I think more likely other cause for your neck itch but needs examination by doctor to sort it out.