What Causes Irregular Heart Beats After Having Sandoz Amlodipine?

I am a 59 female that had a stent in 2012.................then the cardiologist put me on Sandoz amlodipine 2.5 mg daily as I had told him I was experiencing irregular heart beat at night. The past 9 months my family dr wrote the same repeat prescription but changed it to 5mg and a half daily, I asked him why, he said it was because of my blood pressure. I always had low blood pressure, today it was 120 over 56 I think, I am confused.