Yes, I especially have trouble in the winter months when daylight is short. I take mega vitamin D (in winter) and try to walk my dogs as much as possible. It's 2 miles around my block (obviously I live in the sticks!) and once a week we try to go to a park or walk with some human and doggie friends. Even if it's the last thing I feel like doing, I always feel better afterwards. The fresh air, exercise and quiet time do me a world of good. Hang in there...remember, someone always has it worse.
How about volunteering for a cause. My dogs are both therapy dogs and we are involved in a group called Roxy Reading. We go to schools and kids read to them (it helps with confidence and courage. Tomorrow we start a new program and go to the courthouse to help kids who are testifying in court. I always feel wonderful after working with the dogs and kids. Happy thoughts being sent your way!