L.A.
I had a similar situation at 12 months, no problems until then, and then I would get a clogged duct about every other week. I think it could be to the more erratic schedule, as that is when we partially weaned as well, the breasts are not emptied as often or as regularly. What helped me was to make sure I had lots and lots of fluids, as I have a tendency to forget to drink during the day. When it would occur, I would use a sock full of rice and heat it in the microwave to help soften the clog, and then just let my daughter nurse like crazy on the clogged side. I never ended up with mastitis, but it took a few weeks before my breasts figured out what to do and now at 25 months my daughter still nurses once at naptime and at bedtime and in the night. We partially cosleep as well, and this works for us. My milk just lets down when she is ready to nurse, and I don't get engorged if I miss her naptime when she's out with Grandma. I hope this helps somewhat, as it sounds like you might have a similar situation.
Edited to add:
Don't worry about the judgmental post down below, your child will not be sleeping with you when he's 12, and children are not all the same, some need to eat at night. Just like some adults do. This same person gave someone else advice that said to give a one year old 2% milk, even though everything I've read from APA etc. says whole milk till they're 2 years old, then low fat. You're doing a great job raising YOUR child. I think you are teaching him that you care enough to do what's best for him.