Unfortunately this is a common complaint and you should not assume that all custom orthotics are uncomfortable and don’t work. In these cases it is generally the fault of an inexperienced practitioner with limited knowledge of plantar fasciitis treatment and custom orthotic prescription.
Common reasons why your orthotics have failed in the past:
Misdiagnosis of plantar fasciitis
Orthotics with a poor arch contour
Orthotics increasing forces on the heel insertion
Uncomfortable or poorly prescribed devices
NB. There are many similar conditions that can mimic plantar fasciitis symptoms. Unless your heel pain is properly diagnosed by a podiatrist you will most likely end up with a poorly prescribed custom orthotic that fails to improve your symptoms.