I second what @Espiritus_Corvus has said. It’s not abnormal for people suffering depression to manifest with crying, extreme lethargy, physical ailments such as you describe and all sorts of things that lead to feelings of hopelessness, worthlessness, apathy… and worse. Sometimes it’s a transient thing; it goes away on its own. (It’s not uncommon at all for people to feel depression while already afflicted by grief at the loss of a loved one through death, divorce and other separation – and part of what you’re describing can be “normal grief” if you can pinpoint the cause and if it does go away on its own after time, or at least gets easier and easier to deal with, even if some sadness remains for a long time.)
When you can’t say “This is why I’m feeling bad” and work in some way to process the grief, exercise the hormones (by which I mean “exercise the body that they’re in”) and “deal with it”, then it’s time to seek professional help. I would also caution against long-term medication, but not all medication is bad if it helps you “for a few weeks or months” perhaps, to get over the worst symptoms until your body and mind can take over your emotional (and brain chemistry) equilibrium.
Do you have any counselors, a minister or someone else not “a crush” or “an ex” or “a potential mate” (because you don’t want to compound your problems!) that you can talk to for starters? It’s best for this if you can find someone who doesn’t already have an emotional attachment to you, is bound by a code of ethics not to take advantage of you in a vulnerable position, and has some experience dealing with depressed young people. (And someone with whom you’re less likely to attempt a romantic interest. Seriously, because that happens, and it makes things worse, not better.)