I had a baby by c section in September and my 1st period afterwards in October lasted 10 days.In November it lasted 4 days and now this month it has gone for 12 days. Should I be worried?

Not necessarily, some women find it takes a few cycles after childbirth to get back to something more regular.

Is it the same amount as when the period started or has it tapered off a bit at this point? Are you on any sort of birth control and/or breastfeeding? As either of those can sometimes effect your period. You could certainly give your doctor a call and see whether they feel you should go in and get checked.