What Causes Blood Clots Instead Of Menstruation?

hi, my menses starts 5 days ago but only blobs of bloods once awhile and not the usual gush or heavy flow..how's that so? I am 38yrs this year with a 8yrs old child. i used to have this blobbing problems and the flow starts about a week later but the last few periods was normal flow that last about 6days