I also took the mini pill while breast feeding. Just continue taking the pill at around the same time everyday. Your pills should have come with a pamphlet instructions from the pharmacy. That may help answer some of your questions but of course your doctors office should have a nurse available too.
Your body is probably adjusting to the hormones, so just keep taking it and it will even out. The mini pill is progesterone only rather than an estrogen/progesterone combo like the traditional pill, but it's still a hormone so it may take your body some getting used to. You may not get a true period for a while either so don't let that scare you. I didn't get mine until my son started on bottles at about 10 months.
Taking the pill the Sunday after your period helps regulate your cycle. You can really start any day after your period, but Sunday is the easiest for most people.