Hi,
I know how you feel, I am now 22 and have been depressed on and off for about 3 years. The last year has been really bad for me after I broke up with my girlfriend. I've been seeing a counsellor and takking antidepressants for the last 3 months.
Like you I have a complete loss of confidence for a long time and my worries/ anxiety just eat away at me like a viscious tornado of thoughts running through my head.
Relationship doubts are very common but it is certainly made worse by the depression. I had been with my girlfriend for 4 years when we broke up and I think depression did play a part in it, it wasn't the only reason but it didn't help. I was definately pushing her away without even realising it, I just wanted to be alone with my own thoughts and didn't speak to her or support her as I shud. I used to leave myself notes like "I hate my life, no-one cares about me" etc. she has since told me that these made her feel terrible and made her want to be with other people to get the support that i wasn't giving her. I've found that depression makes everything seem negative, relationships, friendships, everything. I think you should maybe try to talk to your girlfriend about ur low feelings. It doesn't have to be a major event, just let her know that you do feel down sometimes. If you do love her when your not depressed say that, it's not her fault that you feel like this it's just the depression that affects ur perception of the relationships. If anything we need more support and help than ever when depressed so if you have someone to talk to or be with try to hold on to that.
On your meds have u tried Citalopram? it is supposed to deal with anxiety and depression. It helped me alot but it did take 4-5weeks to kick-in and start working. Also i don't know if anyone has mentioned it to you but you could have S.A.D (Seasonaly affected disorder) it is a form of depression and directly affects ur mood from December to April/May. Also i found the following website very useful, It gave me a much better understanding of depression, what to look out for, how to deal with it, and the personal stories are very interesting to read.
http://www.studentdepression.org/warning_signs.php keep well
e
"Give me something good to die for to make it beautiful to live"