Is it possible to get a positive pregnancy test followed by a negative test, i think i have a yest infection can that effect the result of the test?

Yes, but...: You can get positive, followed by negative for a few reasons, for example a failed pregnancy (one that did not implant well in the uterus) or pregnancy that implanted somewhere outside of the uterus (like ectopic pregnancy). You should talk to a physician, and if you develop vaginal bleeding or abdominal pain, or other signs of severe illness, go to the er. Yeast will not generally interfere.