Been a mth and 2 days since my gb removal. Why am I still having pain on my side?

Hard to guess. Need to see your surgeon for an exam and full history. Pains can be from many sources; muscles, nerves, back, stomach ulcer or gastritis, etc. I cannot tell without a full medical history & and exam.
When to get checked. I agree, you have reason to get checked by your surgeon. In addition to possible post surgery problems you could have a new or related problem such as gastric ulcer. Go sooner if you have fever or emesis. Good luck.