Have been experiencing burning sensation after peeing for 3-4 days now; i'm expecting my period today but have instead discharged a brown thin liquid?

Something's up!: If it were simply a matter of an abnormal onset to your period, I would recommend a few days of watchful waiting. But, because you also have persistent burning with urination, you should get a medical evaluation. Best wishes.

Burning sensation: Suggest urinary tract infection . See a doctor for urinalysis .May consider HPT if your period dose not come in a few days