It sounds like you have a lot of stress and anxiety in your life. Those tests should have picked up if you had any heart trouble. However, chronic stress can cause your body to react negatively causing weird things to happen to you also. When you are stressed or anxious it causes overexposure to cortisol and other stress hormones and can disrupt almost all your body's processes including your heart beat which can lead to heart disease. To rule out that it is not your heart there is one more test you can take . It is the sleep test. It's done at night in the hospital. It takes a long web cam of your heart beating all through the night. If it beats wrong even 1 beat it will be seen on the test. To me, what you have described it just normal stress that we all have. Working too much and getting too tired can also cause heart problems. Rest is very important.
Did you have any episodes while wearing the holter monitor? If so, it should have picked up any palpitations. Afib would have been noticed as well.
If you had no episodes while wearing the holter monitor then you may need to wear it again and wait until you have an episode while wearing it.