Why do I feel sad/depressed (idk) even when everything in my life is going good the way I wanted it to? Or is it because I'm just overthinking and making up things?

Good question. In my opinion, the main difference between being sad and being depressed is that sadness usually have a reason. For example, if you experience a difficult, painful, challenging or disappointing situation, it is normal to feel down during/after the event but it is something that in most cases goes away in a short period of time. Depression on the other hand is something that seemingly has no reason at all and the negative thoughts can stay with you for weeks, months, years. It can affect most or every part of your life. You no longer enjoy the things that used to make you happy, you can lose your motivation and energy, you can become impatient, irritable or angry at everything. Depression can make you think that everything's gone wrong in your life even though you are doing well at school/work, having a great relationship with your family/partner/friends, etc. The physical symptoms include: change in your weight or appetite, too much or too little sleep, fatigue or low energy, acceleration or deceleration of physical activity. The mental symptoms include: feeling worthless, unreasonable or excessive guilt, being indecisive, having difficulties with concentration, loss of interest. I think it's important to mention here that depression is a mental illness and if you are experiencing these symptoms, it is NOT your fault and there is nothing shameful about asking for help. It takes a good amount of courage to share your thoughts and feelings with a therapist or even with people who are close to you but it can be life-changing.