Well, your eyes will not cry with no reason. And generally speaking, according to your description, you may get dry eyes. And for dry eyes, it occurs, when your tear system has got some problems. Also, in some cases, there are many factors which can lead to dry eyes, including vitamin a deficiency. We can say that you do not intake enough vitamin A, you may also experience problems with dry eye. Besides, if you have dry eyes, you may experience scratchiness, itching and burning on the surface of your eyes. For your situation, I will suggest you go and see the eye doctor as soon as possible, or it can be dangerous.
Tears is normal physiological phenomenon, but if your eyes always tearing for no reason, your conjunctiva must be ill. There are so many reason can cause conjunctiva lesions. The cause of the symptom may be inflammation or infestation, it also may cause by allergic reaction. You could check is there have any red veiny in your eyes, if so you are likely got conjunctivitis. But don't be worry, go to buy some eye drops in pharmacy and remember to go out wearing a goggles within one or two weeks until your eyes feel better.
Ok, from what I can see, there must be something wrong with your eyes, because generally speaking, we would not cry without emotional fluctuations or yawning. I suspect that you have got blocked tear ducts, which results in endless tears shed down your cheeks. Just try to consult a doctor and figure out what to do with your problem. You should pay attention to your eye health in the future to prevent potential problems.