You've done something very dangerous by dropping from 20 mg a day down to zero. Even fairly low doses (4-6 mg per day) for a few weeks cause the adrenal glands to stop working. The adrenal glands don't start instantly working again when you stop taking prednisone - you have to taper off of prednisone slowly to allow the adrenals time to get back to full functionality. Depending on how long you have taken prednisone, that can take several months or longer. In some cases the adrenals don't recover, and the person has to keep taking a medication to compensate for the adrenals.

Here is a quote from Google AI about the risk of stopping prednisone suddenly:

"Abruptly stopping 20 mg of prednisone, especially after more than a few weeks of use, poses a serious risk of adrenal crisis, a life-threatening condition where the body lacks sufficient cortisol. It can trigger severe withdrawal symptoms, including extreme fatigue, weakness, body aches, joint pain, low blood pressure, nausea, and, in rare cases, death. "

In the UK, people taking prednisolone are required to carry a medic alert card in case something happens so that medical personnel know the person is dependent on steroids.

It sounds like you need to be on at least 20 mg for several weeks to get your PMR back under control. I wouldn't try to taper until you discuss it with your doctor.