First, I would see if your parents could at least find room for you and the baby, immediately. Let your mother know that you are stressed and would like to move in sooner.
If there is no way to move in with your parents immediately, then have a heart to heart with your mother-in-law. Let her know how you feel, without attacking her verbally. If you don't, then the next 2-3 weeks will seem like a year. It is her house and she has opened it up to you and the baby. You could very easily take advantage of the situation and let her be the overboard grandmother and get some of the things done you've been putting off. Once you're on your own with the baby, you'll find a little less time for those things.
Just some suggestions. You'll know what works best for you.
