Dear doctors, i'm 19+, having irregular period with period blood which is watery and bright red. last period blood was very scanty & i'm not pregant?

Irregular periods ?: Firstly if you think you could be pregnant , check a home pregnancy test to rule that out. See your doctor for irregular periods. It's very common but need to be treated .

GYN exam: this is most likely breakthrough bleeding mixed with vaginal and cervical mucous. This may be due to normal female hormonal fluctuations. If you are not sexually active, I suggest a call to your GYN.