well it's tricky!
my DS2 was 8 months and 2 days before I stopped DH I had sex, which as it turned out to be is all I needed to get pregnant with DS3!
I had no periods while bf, and I can only pinpoint the exact time I got PG coz we did nothing for 2 weeks previously due to exhausting teething baby and definitely nothing afterwards as I started having uterine cramps literally within an hour after the "event", which were very painful and lasted for weeks!
(having had 2 kids with a 17 months gap I ended up without a period for over 2.5 years, result!
)
the fact that you have cycles already increases your chances already, but as they are irregular maybe you could invest in ovulation testers?
TBH stressing about it will make conception less likely, so perhaps you could tell yourselves that you are having fun for now and will only TTC after DD's 2nd birthday. see if tricking your minds that way and relaxing about the issue might just work?
and really just have fun, do it when you feel like it, not too often but not once a month either, and in the mean time try and focus on something else as well -a project, a hobby, a new class anything!
you've got a DD, no reason why it wouldn't happen again, so just give yourself a bit of time!
and one more thing - make sure you are taking folic acid, good vitamins, iron (so you are not aneamic) and fish oils; get as healthy as possibly with eating & sleeping well and exercising.
that will keep you busy, on top of looking after a toddler!
is that helpful?