You probably don't have to involve your parents, but I'm sure they would want you to seek medical help, and this is a medical problem. There are physical and emotional reasons for depression, and only a doctor can sort them out and get to the reasons for your depression. Possibly you can see your family physician and not tell them why you want to go. Your doctor will keep everything you say in total confidence if you ask.
Your parents do probably want to know if you are depressed, and they would want to know why. I'm sure they've seen a change in you and may already be worried. They may already want to talk to you about it and are afraid of upsetting you, just like you're afraid of worrying them. This is one of the reasons you need an outside person like your doctor to analyze the situation. Parents and children often have trouble discussing health issues between themselves. It's pretty normal. They may be afraid that they are the problem, or they may not be in touch with you enough to realize there is a problem.
I don't know what the facilities are at your school, but even a school nurse will know something that would help. They would at least be able to refer you to more help and also keep it in confidence if you ask. A trained guidance counselor should also be able to help and can get you more help. Even one of your teachers should be helpful to you. Pick one of your old teachers that you like and go have a talk about your problem.
You do need to take care of this problem. If you keep putting it off, it may get worse (for most people it does). You run all kinds of risk as you make worse decisions as time progresses. You can think that you're thinking clearly, but you can be deceiving yourself. And if it is a physical problem, you may need medication. This isn't something you can do yourself. People who try to self medicate themselves in depression always choose the wrong drug. Which leads to more problems while only worsening the depression.
So, you need to talk to someone. I'm not a good substitute. I can give advice, but I can't diagnose any medical condition from here, even if I were qualified to. You should have several choices who you can talk to, and a choice of how much you want to involve your parents. Make an appointment with a doctor. The sooner the better. Please.