Insomnia could be caused by a wide variety of issues. First and foremost, I would highly recommend consulting a doctor to ensure any medications you're taking do not exhibit trouble sleeping as a side-effect.
To tackle the issue, I would highly recommend seeking our guide (Which, is also used in professional settings) located here: https://www.7cups.com/sleeping-well/ The reason I reference this is because insomnia could be caused by many different issues including, but not limited to: stress, anxiety, medical conditions, depression, poor sleep habits, scheduling (work, school, exercising timing, etc), enviornment changes, substance abuse or substance intake (caffeine, drugs, alcohol), eating habits, and so on and so forth. The guide provided helps you identify some of these possible issues and allows you to objectively (partially) view all of these variables. I should note, however, no one would be more qualified than your doctor or professional.
Insomnia is a serious issue because sleep is so important to the body and psych. It can be as simple as shutting your television and electronics to as severe as a symptom of something more serious. The risk factors are also serious, leading to lower performance in your school or professional career, obesity, irritability, "Increased risk and severity of long-term diseases or conditions, such as high blood pressure, heart disease and diabetes," and many other issues.
However, if you're reading this then the good part is you're taking a proactive approach in reaching out. That, in itself, is a solid first step. :)