Mamaheids, I would tend to think that the difficulties you are experiencing weaning from the Zoloft are circumstantial. I'm so sorry you are feeling this way right now.
A few thoughts on the things you indicated you need:
Sleep: Do you stay home with your 2 y.o. DD? If so, try napping with her. Also, you could go to bed when she does a night or two a week.
Exercise: Can you take walks with DD in a stroller/jogger. Getting outside usually makes a huge difference. Depending upon the type of exercise you wish to do, I know some moms can do yoga, free weights or videos with children home.
Alone time: This is the most difficult for me and always has been. My DH is very support of me getting this time, but it's really hard since I have a nursling (now 21 months). Anyway, I've always started small such as doing errands by myself. This could be after DH gets home from work or after your DD goes to bed. On the weekends when your DH is around, if you want alone time at home get him take DD to a park, etc. Also, if you can rely on DH being home for bedtime routine perhaps you could share it those duties. On the nights he does the routine, you could have time to do what ever you wish (NOT laundry, dishes). If you are really lucky, you could get him to do the entire routine until DD is ready to nurse or however you fit nursing into that.
I'm not sure if any of this helps. I know your struggles. I do apologize if the things I mentioned all seemed so obvious. At one point, I had to figure so much of this out with my older child. It's still SO hard.