Why do i become sad for no reason?

Having parents with bipolar disorder and depression leave you quite genetically pre-dispositioned to develop mental illness yourself. However, simply experiencing bouts of sadness occasionally is a normal part of daily living. The concerning factor is that this sadness has manifested into suicidal ideation.
You could do very well for yourself if you started to keep a journal of these moments. When you feel this sadness, take down the date and time, and then write down what is going on... Where are you, what has happened today, what are you anticipating, what thoughts are in your head... This journal will prove invaluable when going to a psychologist for assessment. They may be able to see patterns in your emotions that you cannot easily see yourself, and be able to address whether or not they are indicative of true mental illness, or simple episodic sadness or depression.
You are in the middle of puberty, and it is entirely possible that your hormonal levels are changing right now.
One thing I wanted to say is, sometimes what people perceive as a "sinking feeling" in the chest or sudden sadness is actually a biological response to anxiety. Many believe that suffering from anxiety means that you will feel nervous all the time, but the reality of anxiety disorders is that they manifest in many different ways. It can be from systemic depression like the sinking feeling in your chest, all the way to digestive issues, headaches, body pain, insomnia, frightening dreams and more. You should make sure to journal any abnormal symptoms you experience.
Just know that while it raises your chances of developing a mental illness, having mentally ill parents does not guarantee that you will be as well. Asking for help to figure it out is not "dooming" yourself to a diagnosis or to taking medications. Getting assistance in understanding your emotions and body responses to those emotions can really help you cognitively manage your feelings, so that you do not find yourself getting swallowed up. It also enables you to have someone on your side, if your symptoms start getting completely out of control and you need to be more aggressive with treatment.

Sounds like depression to me. That is exactly how it started out for me. And the fact that your mom has depression and your dad is bipolar is a red flag. Bipolar is totally genetic. My mom and I both have it. You need to tell them that you want to be tested for depression and bipolar. Don't wait. I ruined many years of my life on a roller coaster and I had no idea I even had bipolar.

Everything you described sounds a lot like what I experienced in my life. Your parents condition should be mentioned when you see a professional. And just be honest about your moods and depression.

Wish you the best!

I am exactly like you, except I don't know if my parents have issues, they never went to doctors, but I think they do. Ugh.

well it's normal this is called a depression and almost all people have it from month to month or in some cases daily depending on there welfare and how much of what they wish they got and how well they are satisfied in there life, simply a lot of things in our life let us down for some reason we feel sad because we are unfulfilled with some of specific objects. since your in your high school sometimes emotion and future thinking always make you feel anxiety leading to depression because you are worried deep down on one of the both or sometimes both emotion and future thinking. this and a lot would make us sad, best way is to figure your feelings and why it's causing you sad then move on for solutions