Some people do have real seasonal affective disorder, which is a type of major depressive disorder. Social isolation is a prime symptom of depression, though. Vegan, it's good you are getting therapy, I am wondering what type of therapy your counselor is using? A lot of times people who are depressed respond very well to CBT, as it deals with the negative patterns of thinking that maintain those feelings. Some of the other things I often recommend to adults are yoga and acupuncture. If you can find a Mindfulness Stress Reduction class, that also teaches coping skills that are great for anyone, really, but often give people a sense of peace. This class is often given through hospitals/community education agencies.
Something else that helps to give structure to your day is volunteering. Not something that is a huge commitment, but a lot of the time, helping others helps you take the focus off of your thoughts that are maintaining the depressive feelings.