What Causes Soreness In The Area Around Pacemaker?

I had a pacemaker implanted under the muscle on the left side of my chest about 5 or 6 years ago when I was 20 years old for dysautonomia. I have not seen a doctor since the summer of 2013. Lately the area around my pacemaker is very sore (not sore enough to limit mobility, but feels badly bruised) and I am worried that the pace maker may have moved or may be pushing through the muscle. Is it normal for it to be sore?