All my panties has stains and i don't know the cause of it.. even if i buy new one, just few hours of wearing it the bad smell and colour will appear?

Female discharge.: I suggest a GFYN evaluation. This may simply be normal vaginal and cervical mucous , often related to hormonal/sexual factors; however, a female vaginal infection must be ruled out. Some women normally secrete more vaginal liquid than others. The odor is usually related to low grade inflammation and/or infection.

Agree with Dr, M: An abnormal discharge needs to be evaluated. In the interim you may use panty-liners. These have absorbents and may be deodorizers that may help with the odor issue, in case you naturally produce more secretions.