When is the right time to check pregnancy test?

Kate
I'm 30 yrs old, TTC for 3-4monthd now. I have 3 days delayed (with regulat period and complaining of such symptoms of vaginal pain in urination and feels like i'm so tired and sensitive. I cannot predict if im pregnant or not? 
When is the right time for me to have pregnancy test or blood test to know if im not pregant?