Chronic lower left back and left side pain?

For the last year and a half i have had mild to severe pain in my lower left back and left front abdomen side. For months it was something that came and went, but for the last couple months it has been constant. I have been to 3 different doctors and the ER 4 times for it.. they have done everything from multiple CT scans (with and without contrast), an ultrasound, copious amounts of blood work... and NOTHING, they all show no tumors, growths, or anything wrong with me or my blood work. It is so frustrating to be in this much pain for this long and to have people shrug their shoulders. Now I will say that I dont eat very well, and I (as hard as it is to admit it) rarely ever drink water. Could my lack of water or my poor eating really cause such a large amount of pain and for over a year and a half? Can you think of anything else that may be wrong with me? At this point i just need some sort of direction to go with this because obviously im not getting any better. Thank you in advance!