Hi, I Am A 39 Year Old Lady And For

Hi, I am a 39 year old lady and for about the last 18 months I have had pain which comes and goes on my left side under my ribs. It is mostly at the back but radiates round the side at the bottom of my ribs. Sometimes it feels like a dull ache and sometime like a burning pain. It hurts more when I lie down at night especially on my left side and hurts if I sit in one position for any length of time eg. when driving. I have also noticed that if I sit in certain positions or press where the pain is, it clicks in and out and feels like it's grinding. What could this be? Thank you