It's not possible for anyone to diagnose you over the internet, but the symptoms you are describing do align with symptoms of depression.
I'm glad the serotonin is helping you, but you have the right idea when you mention seeing a therapist. A therapist can help determine what is causing your depression, and what, if any, additional medication might help.
Are you able to discuss this with your parents, or another trusted adult?
My experience with depression and antidepressant medication is the medication does not make me happy, instead it fixes the underlying problem so i can be happy. I still need to do things that i enjoy to be happy, and i am still susceptible to depression if i do not take care of myself and do enough things that i enjoy.
I also learned I'm happy when I'm not wondering if I am happy or depressed. If I am wondering if I am depressed and unsure, then something is wrong.
I noticed you mentioned your parents want you to go to the gym, and to appease them you pretend to go. This makes me wonder if your parents could be causing you stress or contributing to depression. That is something you could discuss with a therapist.
In addition to fixing any body problems (mind/body) there may be other issues to deal with, and those issues could be discussed with a counselor or therapist. (I use both terms interchangeably.)
Best wishes hope you feel better. Oh and i have been surprised how many other people know aboit depression and understand. There are a lot of people who do!
I am going through something along the lines of what you are handling, only when I want to cry, I cant. Mine has been going on for a year now, and I am no expert, but I think the symptoms you present are very clear signs of depression. For the first question where you asked if you should see a therapist, I agree with you and I do think you should. But possibly you could see your school counselor first to see if it is worth seeing a therapist because you might not like it if you do see a therapist and then not be able to leave. I don't have any experience with anything similar to pills only because I don't take any meds, but I wouldn't take whatever you're taking until someone that is an expert or is highly educated with what you are taking agrees that what you are taking isn't harmful and that you wouldn't get easily addicted. I could honestly see anybody getting hooked onto pills that make your mood brighter, for instance, if you feel down and feel like you need more than you normally take you could just pop them. After so many times you could get dependent on them and you couldn't be happy without them, which in other words would mean addiction. I hope that some part of my 14-year-old inexperienced writing helps somehow with your current situation. I wish you luck!