You might also want to go to the doctor & make sure your appendix is ok. The appendix is on the right side, but the pain can be "referred", meaning it can be felt anywhere in the lower abdominal region if it is intense enough.
If your stomach feels tight and gassy with the left side of your lower abdomen hurting, then you need to see a physician for check up and diagnosis. Maybe it can be periods, constipation or gas that has been trapped. I am sure that a doctor will help you much better and give you dietary advice.