Jack Newman has a handout on weaning from domperidone: http://www.drjacknewman.com/help/Domperidone%20Stopping.asp. Basically, he recommends weaning from one pill at a time, taking the new dose for 4-7 days, then dropping another pill. You'd want to keep the # of pills relatively constant over the day, so instead of weaning all 3 evening doses, you'd wean one from the evening, one from the mid-day, and one from the morning, if that makes sense. If at any point you notice a change in supply, you can increase back up to the # of pills just before the supply dip. Many moms, once supply is up to a stable level, don't need to continue at the high dose of dom, but can cut back or even completely eliminate it & baby's nursing will maintain supply.
I don't know if the domperidone is affecting your cycles. It's not uncommon for breastfeeding moms to go a year or more without menstruating. I would think it more likely that your DD's nursing frequency & solids intake has simply reached a point where your body isn't receiving enough hormone stimulation to prevent ovulation. If so, then you don't have to do anything, you'll probably have a period in the next few weeks. Some women do have "silent" ovulations for a month or two without menstruation when fertility returns. You may be noticing this (ovulation). Dips in supply and nipple sensitivity are also common around ovulation and menstruation. From my own experience, this evens out over time & it's the first few cycles that are the most noticibly uncomfortable. If you do experience supply fluctuations, kellymom recommends a Calcium/magnesium/zinc supplement (http://www.kellymom.com/herbal/natural-treatments.html#calcium) that might help.