Ugh. I have similar issues. I'm in my junior year as well and I either get depressed and then stressed and anxious about the work I have to catch up on or I get stressed and anxious about getting A's on everything, which makes me depressed. It's a horrible vicious cycle.

Last semester I started doing something that really helped me. I got a composition notebook. On the left side of the page, I keep a running to-do list of the things that need to get done (ie: pick up meds, do reading for a specific class). Then, every morning, on the right side of the page, I pick a couple of tasks that I can realistically complete that day. I try to break down the bigger tasks from the left side into manageable chunks (ie: if "Read Shakespeare's Henry V" is on the left, then the task on the right may be "Read up to Act 3 of Henry V") This helps me because 1) it feels less overwhelming to see a tangible list and 2) I get HUGE satisfaction from crossing things off my daily to-do list and my weekly to-do list. Setting the goals in the morning, every morning, really helps me focus on what needs to get done every day.

Good luck! I feel like it's about finding a system that works well for you. And make sure you reward yourself too!