How can i tell the difference between psychosis and bipolar?

Depends: Psychosis is a set of symptoms of an illness, while bipolar disorder is an illness with different symptoms. Psychotic symptoms (including delusions, hallucinations and disorganized thinking) can be part of the bipolar illness during a mood episode, but they can occur with other illnesses too.

Symptom: Psychosis is a symptom of multiple illnesses such as depression and schizophrenia. Bipolar is a mood disorder involving both depression and mania and psychosis can be a symptom of either mood swing.

Some overlap: Psychosis means a disturbance of the perception of reality, such as hallucinations of paranoia. This can happen with bipolar disorder too - but with bipolar the primary symptoms involve mood changes -episodes of depression and mood elevations.