I am really concerned about you, S.. I am putting you on my prayer list today. It sounds like your stress level is way over the top and you have hormones trying to straighten themselves out on top of it, a lot of extra people around but no one supporting you. My bet is tht your 3 yr old is simply mirroring what she's seeing in you! 3 yr olds are incredibly sensitive, intuitive creatures. Also may be feeling neglected emotionally, which is your situation as well, of course!
First of all, if you believe in prayer at all, I'd start there. Second, I'd see if you can get an appointment with a therapist and ask her/him about a referral to a psychiatrist (they usually work in partnership with one) so you can be evaluated for medication if you need it. It may only be situational but, even so, meds short-term might help. You may not need them if you can get someone to listen to/support you, which will give you some HOPE, something that is in short supply for you now but is vital for your survival.
Third, make a list of what's stressing you and what resources you have, and see what can be done about any of them. Prioritize and tackle 1 or 2 things that are do-able immediately.
You are going to get through this but you have to stop, ask for help, evaluate, and take some action to stop this crazy mess you're in. Why do you have out of town company? Can you take a break from day care or hire someone to come in a couple of hours a day to give you a break or at least help? (My neighbor did day care and used to have me come over when it was just too crazy, so she could take a shower and re-group. I was just glad to do it.) There may be people in your life who could help but you don't ask and they think you have it all under control. NOT!! You may reach out and not get the help right away, but don't give up.
I went through something like this and realized I had surrounded myself with people who just weren't going to help me. I got into therapy and began to sort out my life. Actually ended up going back to school and separating from my husband.
Plese don't let your life spin out of control. Take a deep breath, ask God to help you, make a good list, evaluate, and get some help you can count on.
God bless you! I'll be praying for you.