Whoa guys, I used to be the kind of person that gets depressed very easily, it's was just in my brain, the way I was since I was a child. When I was 16-18 depression was really bad, I overcame that shit with my parents' help. I don't have depression anymore, it's been like 8 years since that, it's hard but you can overcome that shit, go seek professional help. To be honest I was against seeing a professional and I never did, but now I think it's better to go to a pro.
Nowdays whenever I feel bad about something which is normal everyone feels sad sometimes, I just realize there are people with 10X problems I have, I still feel bad lol but I come up with ways to overcome those problems.
Yes, I know it has nothing to do with external life influences, this is very true, it's in your brain, but you don't need to be like that all your life. Right now I love my life, my family, I got an engineering degree, been dating nice girls, I keep good friends by my side and try to enjoy life as much while I'm responsible as an adult should be. I'm still a tad insecure as I always been but I just deal with it lol.
Hope my post can help you guys out there, remember it's in your brain as you admitted and most problems are temporal. If you feel bad all the time go and seek help.