Melancholia is no joke, it disables people literally.
Others have already suggested seeing a doctor or medication, but I suspect you already have. Personally, I think that medication can only be a short-term option,but it is very individual. My own experiences with anti-depressants (all modern) have not been pleasant , substantial physical side-effects to say the least.
Talking is important, but if you know what is wrong with you then this may also be of limited use. Depression is a very evil disease because it builds on itself and becomes like a habituation,routine that destroys all pleasure. So what to do?
Exercise is very beneficial indeed and it doesn't have to be ambitious but it must be regular, anything that changes your routine is also very helpful in pointing you in a new direction, change something in your daily routine. Make yourself do something you haven't done before and you may well find benefit&encouragement from this. Others have suggested religious help, might be good if you are so inclined although you don't have to be religious to be good!
Diet too is very important, plenty of variety,plenty of change and some basic vitamin supplement (nothing over the top needed) Your friends are vital, but I know from personal exp that I didn't want to burden them up too much, they can feel very helpless if you are very depressed. Just remember, they care about you and you are important to them as well. The past cannot be changed, it makes our present but it does not have to determine our future. Finally, you post on a knifeforum, isn't this a fantastic and interesting place to be?? You get information here, ideas and yeah vitriol&abuse that really comes like a breath of fresh air. Good luck, go forward, anything may happen!
