Thanks for the query at DoctorSpring.com.
While on the pill, it is more often the norm to experienced diminished / scanty bleeding, sometimes only spotting.
The pill is known to gradually decrease the amount of bleeding , sometimes you might even skip a period, so do not worry.
Just because you have sometimes taken the pill erratically ( forgotten it once in a while ), it is worthwhile taking a pregnancy test to exclude a pregnancy.
Try and take the pill sincerely, though, to avoid scares. Once again, I would not worry about the mild spotting, as that is normal.
Please feel free to ask for further clarifications.