*hugs* to you OP. Pregnancy is rough all on its own with the hormones, without added stuff on top!
I don't know how similar SAD and regular depression are, so what worked for me may be irrelevant for you. But, anyhow, I have chronic depression that flared up right after the end of my first trimester. I was having intrusive suicidal thoughts and lethargy. The intrusive thoughts, for me, are always a sign that I have been neglecting my self-care. I was considering anti-ds, and my therapist was supportive but also reminded me that it would not be a substitute for self-care. So I decided to focus on that first and if things weren't better in a week or two, to go on anti-ds then. Anyhow, the self-care helped to the point that I didn't feel like going on meds was necessary, although I'm still open to it.
This is what helped me:
-taking my vitamins, and some extra b-complex
-just getting out of bed the first time I wake up, which for me is somewhere between 6:45 and 7:30. I then try to get outside for some early morning fresh air and what little sunshine there is (with DD if she's up, by myself if she's not). In the evening I am ready to drop by about 10-11pm so I go to sleep. It turns out I don't need nearly as much sleep as I thought I did as long as I'm getting it at the right time of night. Otherwise, I was feeling like 10hrs wasn't enough.
-exercise, a walk anything. I started out by just telling myself all I had to do was go outside and then I could pat myself on the back for doing something positive. Then, the next day, go for a walk around the block. A couple times I felt just awful and I told myself if I could go outside to the end of the block and back and still felt awful, I could get in bed. Sure enough as soon as I got moving I felt just a little better.
-getting a little break away from kiddo any way that I could - I swapped babysitting with another mom and tried to get my butt out of the house when DP was home on the weekends. Also, I scheduled myself showers three times a week, because I was forgetting, and I've been taking lots of nice smelling epsom salt baths just because I like baths.
-we transitioned kiddo to going to bed on her own, and that helped a TON. If there is someone you can pass the buck to wrt bedtime, DO IT. :)
-increased my therapy visits to 1x week - probably will be able to go back down to every other week soon.
-made more of an effort to be social
-cooking a bunch of stuff at once when I am in a cooking mood, so that when I was feeling worn down DD and I could just heat and eat.
-remembering that if I can do something, I would do it. DD spent a lot of days just playing by herself while I laid on the couch or zoned out on the computer. For a while I felt really guilty and awful about it, but the guilt wasn't helping me feel better and be the mom she needed .... it was just making me more depressed. So I decided that I would consider it a good enough day if I managed to get food on the table and keep me and DD alive and that I wouldn't waste energy on judgment. As I felt better I was able to get us out of the house more, play with her, and be more the mom that she is used to. The house also got really messy and it didn't get better until I started to feel better. At that point it was a snowball effect - the better I felt, the cleaner the house got. I'm saving money to hire a house cleaner after I have the new bb, because the house being in shambles contributes to my malaise.
-I also started tracking my moods in a notebook. This was mainly so I could determine if I needed to go on meds by giving myself a more objective record than just my memory. But I found the very act of recording how I felt ("sh*tty," "okay," or "good"), as well as few brief notes about the day, helped tremendously. For instance, I could see in my notebook that days I went for a walk more more likely to be "okay" than days I didn't.
I don't feel like I am totally over the hump right now, but I feel a lot better than I did a month ago, when I was so drained from dragging myself through the first tri that I could barely see straight.
Hope you find something that works for you.