I Am A 40 Year Old Female, And Have Been

I am a 40 year old female, and have been taking OTC Ranitidine for heart burn for the last 10 days. I had abdomen ultrasound a month ago and all were normal. Noticed constipation recently and for the last two days I have felt pain on the left side, lined up at the same height as belly button, and 3 inches from the left side. The pain just comes when I am in the bathroom applying pressure to do my number 2. Otherwise fine, and the pain gradually fades after relief and takes about 10 minutes. thanks for your help.