Is it normal to have feet swell on Methadone? ?

I was started on Methadone for treatment of cervical pain and started taking it Friday. Tonight, I noticed that my feet and ankles are a little swollen, like they were sprained or something. Does anyone know if this is a normal side effect. I am taking 5mg every 8 hrs, which is a small dose, and my doc said the worst thing that would likely happen was a little nausea and constipation, which has happened, Prior to this, I was on ocycodone, 10 mg x’s 4. This never caused any swelling…
I have researched this and some sights, like drugs.com do not have it listed as a side effect, but some do. I will call my doc in the morning because this is actually helping my pain significantly, but there seems to be no consensus on the foot swelling…