Hello~It sounds like it could be a few different things. First, have you had your hormones tested, depending on your age, you could be going through either peri-menopause of menopause, both can sure cause a lot of emotional ups and downs. Second, your blood sugar, high or low blood sugar can cause feelings you are having, I would ask for an A1c test, this tests shows what your sugars have been doing for the past three months, it is one of the best for testing for diabetes. Third, I would also ask for a complete blood panel, this will test everything such as the thyroid, liver, and gall bladder, also, one for cortisol levels. In other words, I highly suggest you see your physician so that you can get to the bottom of this.
In the meantime, I would start taking a good, high potency B complex vitamin, a good, high potency multi-mineral capsule, and Vitamin C, these will help with the nerves and also keep your immune system strong.
I hope you feel better soon.
Have you been to a doctor in those three years? Do you feel this is more emotional things causing the symptoms or a physical condition?