Everyone has good and bad days, blue days, sad days, anxious days and it's normal. Clinical depression is going to be more constant and more severe. There is something called dysthymia which is a low level of depression every single day. Regular depression is more severe with symptoms like not wanting to do things you enjoy, withdrawing, losing hope, trouble sleeping (either can't sleep or you want to always stay asleep), etc.
To me, you sound like you are going through normal stress. And this is good, you do NOT want depression. So, think in terms of how to relieve stress. Sometimes with things like school work, proper preparation helps. Studying as you go, signing up for group study sessions, staying organized so that you don't feel overwhelmed all can help. Keeping your schedule such that it isn't too overwhelming also helps. Also, keep a bit of time every day for exercise. This is a natural stress reducer and releases chemicals in the brain that keeps us more calm and regulated Eat well. Don't give into junk eating or comfort eating. Even if you have a lot to do, try to get proper rest as well. Listen to calming music. Reduce stress where you can and have control such as keeping drama to a minimum in your life. Keep a journal of what triggers you.
But I do believe what you describe is perfectly normal. good luck
Brooding can increase stress. School can become very stressful, especially around exams, when one feels their entire life may depend on how well they do, which turns out to be bogus.
I've learned when faced with this, what seems like a problem, "If only I can do well on this exam, THEN I will be OK." Turns out I actually have TWO problems. The first problem is whatever I am facing (exam, life event, anything stressful), and the second problem is my emotional REACTION to this first problem.
The first problem may be out of my control. My second problem, however, I CAN take control of. I can work to counter my emotional reaction to life events and things which can be stressful.
That's the secret I figured out.
Brooding and endlessly worrying is a very common cause of stress. So I learned (or was taught) to take breaks from worrying. Mind needs a break.
Mindfulness Meditation is one way to train your mind how to take these breaks. Start with just one minute breaks and return your focus to the present moment. When your mind wanders, bring it back to the present moment. Just keep doing that.
It's a good skill to learn.
There are free apps you can download that will give guided meditation breaks. (Headspace is one app I use.)
Practice this whenever you have a moment. After a few weeks you'll start to notice a change, as anxiety decreases.
Being depressed can be a rollercoaster, or it can be a mild annoying background of something is wrong even though everything is fine. I had it for a very long time, so long I just thought it was normal and everyone felt like me and secretly his it like me. Doctor had a hard time convincing me to try medication. If this is normal I don't need medication. Doctor had a hard time convincing me my normal wasn't normal.
She of course wax right. I realized that after I got well. Then I thought, Oh, so THIS is what normal feels like! Yes, definitely MUCH better!