I feel so blue that i don't feel like doing anything. is this depression or just laziness?

It depends on a variety of factors. If you've felt this way for quite some time now and you also feel other typical symptoms of depression (such as changes in sleep and eating habits, recklessness, etc), then you could be starting to develop depression. If it's a passing feeling, then you're probably just feeling a bit more unmotivated. The only way to know for sure is with the help of a health professional, though. I hope my advice was helpful :)