different readings from left arm than right arm

My BP is different from each arm.Left is always higher.I am on Lisinopril 20 mg 1 time a day.This has worked for a few years.I go to a clinic that I never see the same doctor twice.When checking last time and every 90 days for last year or so my readings have been different like this.L arm 138/88,140/90,135/86,145/92 and the R arm 120/80,130/85,120/76,125/82. Tonight my nurse friend checked and my right arm was 120/80 and left was 140/90.I had her do it again R 120/78 ,L 138/88. Frankly things I been reading scare the hell out or me,I need to hear what this can mean in laymens terms. The doctors at the clinic will not take the time to talk,when I asked about this he said,"I do not care about the readings,why are you here".I was there to renew my BP meds.Can anyone help me here, what the possible causes are for this fluctuation could be so that I can be better informed next time or change back to different clinic.I can not afford insurance.Thanks!