I go through that sometimes. And then, I go through periods where I can't stop crying. Both (inability to cry and inability to stop crying) are common in depression. Some people (like myself) go through periods of both while others seem to experience one more than the other. If you know you have depression and are speaking to a therapist currently, I recommend bringing this up in therapy. If you aren't speaking to anyone, it might help to do so. A school counselor, close friend, or a pastor/priest if you're religious might help if you cannot afford traditional therapy. If anything, we at PC are here, too and are more than willing to give you as much support as we can if you wish to talk.