juggling mom life

I need some advise. I have a 3 year old son who just started part time preschool and an 8 year old step son we have everyother weekend. my husband works 6 days as a mechanic and I work 3 days as a hairstylist. my mom watches my 3 year old when I work, the great thing about my job is the flexible hours! the problem we are having is that I really want to have another baby. we do not live a lavish life, we live within our means.. we can afford a modest life cause we don't buy expensive things and buy used as much as possible. I know we could not afford for me not to work at all but I have such a strong desire for another baby but I want to still live comfortably and not have to struggle to get by.. i hope this makes sense, but I am just so torn cause I know the baby stage. but I think long term it would be so worth it. how do you working mom's do it? or does anyone have some advise for us?