What Causes Tenderness,bloating Of Stomach And Back Pain?

I have been getting gas bloating and tenderness on both sides of my stomach below the ribs. Sometimes lower back pain. I quit smoking 2 years ago and have gained atleast 30 poands since but my stomach evrn bloats when i eat a salad. I am 34 years old. Also I have been sitting behind a desk all day versus I used to be on the go.