No Tracy it isn't possible that you make bad milk
it is possible that your kids have not the greatest digestive systems, but not that your milk is bad - YOUR milk is the very best thing for YOUR baby.
MSPI = multiple secondary protein intollerance ie intollerant to proteins you eat (usually culprit is dairy and soy) something to check out on the allergies board.
As to some feeding management...
I wouldn't time how long you feed on a side for, let Evan feed on one side for as long as he likes, maybe putting him on the same side again when he bobs off. Try some breast compressions to speed things up a bit, and get as much hind milk (the super good fatty stuff) out (see
http://babywhispererforums.com/index.php?topic=88759.0) I still do them now when Norah's getting impatient. Then once you're pretty sure he really has had a good go on that side, and only then offer the second. He may take it, he may not. Either way is just fine. A foremilk imbalance wouldn't be just the odd green poo, most babies will have the odd green poo.
Incidentally, read this too about gas
http://www.kellymom.com/babyconcerns/gassybaby.html it may give you some more ideas about what and why.
I was reading up on Lexapro, Dr Hale (the big guy on medication and breastfeeding) does have some questions about its use with breastfeeding mothers, but more about it causing restlessness and bad sleep than digestive issues. Read here:
http://66.230.33.248/discus/messages/43/184.html?1217428044