I didn't read the entire thread, but i also would like to say a few things, the first is that is totally okay to feel sad, like, its normal to not feel happy all the time, right? but feeling sad all the time, doesn't feel good either, if you're sad to the point of not feeling motivated to do anything, or if this sadness makes even your happy moments feeling like black and white, or if you even have some more stressful cases like anxiety attacks and shortness of breath maybe you should try going to a psychologist, therapist or psychiatrist (i dont know which one is the right one).
I once had a pretty gloomy period in my life, when i was sad over a personal situation, and never felt "trully happy" about my conditions, i would often feel like crying for no reason, have anxiety attacks, and even when i suddenly felt happy, accomplished and motivated for no reason, this would last just for some days until i return to my previous state, that made me search for escape routes in addictive habits (i never used drugs thought).
When i used to be like that i was always like, "this is ok, its normal to not feel good all the time, life is just hard like that, and there is probably nothing wrong with me, other people may feel like that as well". But once i get past that situation, looking back at my state, i realize i was really sad, probably way too sad, and sometimes when you're in the middle of the fog you dont see the fog itself.
I am not saying i had depression, i dont know, all i know is that i was way more sad than normal, and i didnt realized it, because i thought feeling sad like that was a trace of my personality, and i should feel unhappy like as if it was normal.
but even if that was not depression, i would still had gone to a doctor if i had the chance, i am to poor, so i cant afford one, but i realize the importance of these guys, some times you need help, even if its something you think its small, i still have some addictions and habits from that situation that i didn't dropped until today, if i could had asked for help things probably could be different now.
So the thing i say to you is, seriously, if you feel like it, go to some of those psychologist, therapist or something, even if you think its a minor thing, a friend of mine ended up discovering he had dysthymia (some type of depression), and overall, he looked pretty much like a normal person, he made jokes, he laughed with me, and he even played a lot whit his friends, but we never know, depression is a serious thing, and even if you don't have depression, its still worth going to a doctor to talk and learn more about your feelings and yourself.
Still, if you're going to a doctor or not is up to you, i am just i guy in the internet...