You cry easily likely because you are an emotional person. Some people are just more emotional than others. To prevent yourself from crying so much, try to not take things personally. Separate yourself from situations so you do not feel emotionally involved. If you are experiencing symptoms of depression, such as sleeping a lot, gaining weight, losing weight, or not being able to concentrate, see a doctor.
Emotions are an important facet of human existence. I think every person deals with that differently. I would(and do) guess frequent crying is a strong indicator of being overwhelmed.. It might just mean you need more or more appropriate support. (Everyone needs support!) Some coping techniques might be but are certainly not limited to: keeping a journal, exploring a creative outlet, confiding in (but not dumping on) friends, a religious or spiritual practice, reducing your commitments, seeing a licensed therapist or even exercise. Try to find activities that help you relax, feel empowerment and offer you a little perspective from the stress you feel. Stay strong and have faith in your ability to reckon with this. New habits and perspectives are easier to develop than it may sometimes seem
While emotions are a part of the human experience, they can become overwhelming.
What you are mentioning could just be a part of your psychological make-up, assuming that this has been the case since you were young. Feeling more emotional than usual could also be a reaction to life stressors, which happens to everyone at some point. However, if this represents a change for you, you should know that this could be a symptom of depression or another common mental health or medical condition.
Depression is a medical disorder which is very treatable through medication and psychotherapy, but it doesn't often just go away on its own. Contact your primary care physician to get more information about your options. A doctor can also run some routine tests to ensure that a medical condition isn't causing your distress. If you don't have a doctor, know that in most areas there are community mental health clinics where you can get services either for free or on a sliding scale. This website: http://www.nami.org/ has good information on common mental health conditions.
My grandma calls this "pisher in the eye." And, it runs in my family for some reason. It is not necessarily crying out of sadness, and in fact, many times can be crying out of joy. I've never thought to look into this, but it could just be a hormonal imbalance: http://www.holistichealthtools.com/truth-about-progesterone.html
If you are sad and crying all the time, this might be different and maybe worth going to see the doctor about.