I had similar issues with my daughter - who is now 13 by the way! Dr. started me off with Nutramigen to supplement my breasfeeding as well... way too expensive! We switched to Good Start - best thing we ever did!! It worked even better than Nutramigen! We used the powder so we were able to use filtered water when we made the formula.
Target has Good Start on sale sometimes too!
Warning: Do not put your child on soy unless you absolutely have to... soy messes with the hormones.
Side note: my daughter's stomach issues ended up being that her body does NOT produce enough acid, so we need to give her a pill with the stomach acids in it 15-30 minutes before she eats a meal. Works like a charm! This was discovered by a chiropractor after being mistreated by various top "Blue" GI specialists who even operated on her to stop her reflux when she was 10 years old - waste of a surgery! Yes, your body will reflux when it doesn't produce enough acid...
I commend you for still BF while working... that is a awesome commitment!
Enjoy your baby! Hope this info. helps!