Gaby, sadness may well be the cause. As Walt said do the Structured Educational Programme, it will lead you thru all the possible reasons for your pain - it will be a combination of your past experiences, particularly as a child, and the things that have 'triggered' your symptoms since, and your own personal characteristics. As you do the programme - day by day you will discover why you have pain and you will learn what tools to use to heal yourself. (journaling, meditation, mindfulness, life changes, attitude changes....) You will find the things that work for you - and you WILL be able to overcome your pain. Have faith and take it day by day.
Two years ago I was a disabled person of 22 years - now I am a hiking, cycling, landscape gardener ... and it started with the Structured Educational Programme.... and Dr Sarno of course!!