Are my feelings and emotion changes for real? or just in my head? (psychosomatic) i feel sad most of the time, yet, nothing causes it. it just happens

Something causes it: Yes, it is in your head . . . and in the rest of your body. If you feel sad most of the time you may have a depressive disorder, the symptoms of which can be relieved/eliminated by revising troublesome thoughts, changing mental focus, and increasing healthful behaviors. Look for self-help materials on Cognitive-Behavior Therapy and Positive Psychology. Or, see a professional.

They are very real: Feeling sad most of the time is a symptom. It is real. From what you say it is hard to know its cause but it should be taken seriously. At minimum you should see your doctor for a checkup and be evaluated by a psychiatrist. Even if the cause is psychological chronic sadness is a very real problem and deserves good care.