When i started antibiotics, my cold sore went away. but then it came back. i use antibiotics for infection in theeth. why wont the cold sore go away?

Likely hsv: Cold sores are usually caused by HSV (herpes) though some can be from other viruses or not from an infection at all. Herpes is not treated with an antibiotic but with an antiviral medicine like acyclovir. Herpes is for life--once you have it you will always have it and though an outbreak can be treated, it can come back again and again, often during times of stress. This may be what you have.

Cold Sore is Viral: A cold sore is viral in nature and not bacterial. Antibiotics will not resolve them. They go away in about a week and since most antibiotic treatments are also about a week long, the first sore just happened to resolve on its own around the same time you finished your antibiotics, but the antibiotics probably had nothing to do with it. Denavir (penciclovir) is a good topical medication for cold sores.

HSV 1 and HSV 2 : Herpes simplex is divided into two types: HSV type 1 and HSV type 2. Both of these conditions can affect your mouth or your genitals and can be spread via oral sex, but not trough clothing. There no cure for HSV infection and often stress is an aggravating factor. Cold sores generally clear up without treatment within 10-14 days.