To be honest I was kind of waiting for someone else to reply to you as it feels just wrong if it tends to be me all the time! So first, a massive congratulations on the birth of your daughter, as this is such a special time for you all.
I'm afraid I don't have direct experience of SAD, but as you have done suggest you learn as much as you can about the condition you think you might be suffering from. You may also wish to register here: https://www.mentalhealthforum.net/forum/
(Dear Moderator, please don't remove the link!)
As there is an entire forum dedicated to Seasonal Affective Disorder under the Depression Forum.
For what its worth, I do think it is the wrong time to make a major decision relating to your employment right now. The first few months (I'll try not add years!) looking after your family as well as embracing change are tough, so putting a big decision on hold for a while, (thereby maintaining some continuity) whilst you recover and have moments of clarity would be my suggestion. As to would be literally ripping the knob off the self care activities such that you do as many off and as much off as you can whilst continuing to support those around you.
Ultimately though these decisions are all yours, ensuring that you are in the right place to make them in the first place demonstrates great insight.