Hey there -
I posted a similar question on this board some months ago and got some good responses from mamas who have done it and how they managed. I am in a similar situation as you are. I have 2 boys, ages 3 & 2, work full time out of the home as a health care professional 45-50 hours per week, and am expecting my 3rd in December. With DS1 I took 12 weeks maternity leave, with DS2 around 6-7 weeks maternity leave.
Recently, however, my family and I have decided to move in order to lower our cost of living, thus allowing for me to switch to part time. Starting in late July I will go to 24 hours per week. We made this decision mostly because I have been unhappy as a full time WOHM, but not because I don't think it can be done with 3 children.
Some of my challenges have been the cost of full time child care (we live in a very high cost area and do not have family to help). And generally being unhappy about being at work. Some of the things that seem silly but have really worn me down in the past 3 years is the whole get them up ready and out to daycare, by 7:30am, constantly supplying disposable diapers, wipes and pull-ups to daycare (they won't do cloth which is our preference). After 3 years now of spending only only 2-3 hours a day on weekdyas with the boys, I am ready for something different. I do know plenty of other mothers who have been happier, than I working full-time. Alot of times that have a nanny, or are able to have family help with child care, and most times they have work that they love.