I usually have heavy blood flow during menstruation, however for this past two days, my blood flow is very light. is it something to worry about?

Could be: A menstrual period that happens on time but is much lighter than usual could be an implantation bleed rather than a period. If you have been having unprotected sex, you need to do a pregnancy test and repeat it in 3-5 days if it is negative. There certainly are other things that can cause a period to be lighter but most will also cause it to be irregular. Hope this helps.