Are you feeding it and if so what with and when?

I have a feeling that your problem is in this department.

For example my plants thrive on neglect, they only get fed if I am fertilising something nearby.

I am not saying this is the best method, but as I said,I think it is a feeding issue!

Is this a herbaceous paeony? Planted/replanted five years ago? Often the non-flowering is because it has been planted too deeply - the resting bud (in the winter) needs to be above the soil.
If this is the case, wait until all top growth has died in the late autumn and immediately dig it up and replant at the correct level. Paeonies start into growth (underground) very early in the season so any replanting should be done as soon as they go dormant

Paeonies can be remarkably sulky and sometimes take years to flower properly. I brought one here from the UK over six years ago, and it's only this year that it has flowered with any enthusiasm for the first time. I have to say that it was worth the wait (but only just).

Other things to check:
Has the soil grade been changed?
Is it getting enough sun? Or has a young shade tree started to cover it, or a new shed?