when do you know if it's just a period or a walk miscarriage your having?

I kind of worried cause what I tho maybe my period started 35 days from my last period (whuch was may 13th)

with that being said normally my periods range between 24-27 days every month . I have never had a period be this late . and today I had notice some pain where my c-section scar is its not like cramping I normally have but I don't have an pelvic pain beside my private area feeling stingy ... how would I know the difference between if it's just a weird period or was a early miscarriage? any help will be greatly appreciated