Usually what happens with an overstressed Mom is that she just stops making milk! The baby gets less milk when nursing, and THAT makes for a cranky baby. The absolute BEST thing is enough rest. Nap when the baby naps, if at all possible, is the best advice. That's fine with the first one, but each subsequent bambino makes that suggestion harder to follow without some help around the house.
I work with a gal whose 2nd child is about 18 mos now and they're having a terrible time with their oldest who is 5. The 5 year old has terrible allergies, had terrible excema as an infant, his teeth are malformed and has 12 fillings already. Behavior problems are showing up at school and I suspect learning problems will follow. I blame it all on the mother and her diet. I watched her during that 2nd pregnancy- it was a "cheetos and pepsi" diet with the occasional prenatal vitamin on top. She ate crap while pregnant, fed her infant crap, and now her 5 yr old will only eat crap (chicken fingers and french fries). And she'll bore you to tears with stories about all her kids' health problems and how the doctors just don't know what's wrong.
Sometimes I feel totally insane: Why am I the only person who sees this connection??*
*I know I'm not, but.... ;)