couple of thoughts.....

I like danniellabella's suggestion - he could be a little hungry, growth spurt perhaps?? Maybe start with this one first......but even teething can cause things to go slightly off kilter

or

if you feel comfortable with this, you could help him learn not to need his dummy. If you are comfortable with this, I'd start with day naps first easier and shorter time frame so not such a hard slog iykwim?

hth