How do I know if my insomnia is a symptom of a bigger problem, like depression or bipolar disorder?

You can know this by visiting a doctor. You can also know it by reading the "Sleeping well guide" which provides you advices and information about sleeping disorders

Seeking advice from your doctor would be the safest answer ! Non thinking tools and exercising can help change sleeping patterns 😴 heat pack across your eyes and warm milk might help too ...

When I start wondering about this, I try to look at how long it's been lasting. If it's only been for a week or two, I kind of wonder if I'm anxious about something or has my routine changed. If it's happening for more than a few weeks, that's when I generally go to the doctor and ask for their opinion.

Taking a step back to realize that your insomnia could be part of a bigger concern is always the first step. Sometimes talking to someone about what is happening in your life can help you realize that you are more troubled than you might have thought. I find it's important to look at reliable sources for other symptoms of disorders, or refer to the APA's DSM (American Psychological Association's Diagnostic and Statistical Manual) which is used for diagnosing disorders.

Depression (and I'm sure bipolar disorder, as well) can cause insomnia, however insomnia can cause depression, too. If you find you have symptoms that match those listed under the 7 cups depression self help guide or on a psychology website, you may have a correlation between insomnia and the bigger picture, however without a professional opinion, you can't know.

For these types of questions, it is best to consult someone with a professional degree. It might be beneficial to consult with your doctor or a registered counselor before jumping to any conclusions.

knowing and being aware of my thoughts when i go to sleep. If my mind is racing about random problems and having no solutions i know i need to reach out for help.

If you're questioning something about your health, It's always best to talk to a professional. Call your doctor, and set up an appointment with them. Or talk to a trusted adult

The best suggestion I have would be to talk to a professional so that they can talk to you about the possible cause of insomnia

Going to the doctor, psychologist or psychiatrist would be a good idea than self-diagnosis. It is proven risky especially if you do not have a background or sufficient knowledge about mental health.