Multiple symptoms: weak immune sys., gastro prob, neuro sym, malaise, fatigue) for over a year but still no answers & losing motivation.any suggestions?

In the absence of: A diagnosis one must go to the essentials. How is your sleep at night? If fatigued during the day, can u nap if given opportunity? How high is stress and worry? How high are feelings of sadness and guilt. You may need a top down approach lest you be doing labs forever. If negative workup may need top down approach. It's quite easy, in fact, to treat if that is the issue, I do it every day.

CFS or depression?: You've probably already looked at chronic fatigue syndrome and depression. While you continue to pursue the answer, do everything you can to ensure you're getting good quality sleep, while minimizing stress. Otherwise things are just likely to get worse. You have to take care of yourself or you won't be able to help others.