hi Jon, welcome to PC

If you're feeling depressed, the best thing to do is get some help. Depression is very treatable, and the earlier you start treatment, the better. Plus, you may want to get checked out by a doctor to rule out other causes for the way you're feeling, like thyroid problems. If you're comfortable talking to your mom, then I think you should tell her how you've been feeling. If she has been on antidepressants, she will probably have a good idea of what you're going through. I was so nervous when I told my mom I thought I was depressed, but she told me she'd been on anti-depressants for a while in the past, which I didn't know until I brought up my own depression. Just make sure that when you do talk to her, you are gentle about having found her medication -- she may be sensitive about having needed antidepressants, and it may not be something she's shared with many people (in my mom's case, she didn't even tell my dad).

Good luck, and keep us posted on how you're doing.