Hi ilmamm - you sound like you are describing depression. I am not a medic but have a fair bit of experience of mental ill health, especially depression and anxiety. Sometimes if the stresses and strains of life get to great, it can cause depression, and I honestly think that you are experiencing the first signs of depression, probably quite mild at the moment, but I do urge you to see a GP and tell him/her how you are feeling and you won't be telling them anything that they have heard many many times before.
It is a symptom of depression that we feel we should be able to do something to make us better, and unfortunately this isn't completely true. I am a firm believer in ADs as they have been a life saver to me. Once your mood has lifted, then there are things you can do to help - nothing unusual really, just making sure you get some exercise in the fresh air once a day, not isolating yourself (we want to withdraw when we have depression) and there are times that it is ok, but we also need to try to get going and not isolate ourselves.
First things first, I think you need to see your GP. Most of them have a sort of checklist and they will ask you questions about the major symptoms of depression and score you, and then decide whether you are mildly, moderately or severely depressed, and take whatever action is necessary. Mostly you will be offered ADs and possibly counselling but there is usually a waiting list.
Kepp posting............there's lots of support on here and you are certainly not alone - it's just so much worse than physical illness isn't it because people understand that but so many don't understand mental illness, and that makes it worse.