Tummy issues

Our LO is 4 weeks today and she can get so fussy.  She passes gas and poops fine but she seems to be in pain and spits up a lot.  Even so, she's gained 2 pounds.  Anyway, hubby is so overwhelmed with the way she gets upset and has insisted we try formula (she's entirely breastfed) and I'm heartbroken.  I really hope she isn't sensitive to my milk :( we've been given Zantac from the pediatrician.. Hasn't seemed to help.  We've tried gas drops.. Doesn't seem to help.  I've cut dairy products from my diet.. Doesn't seem to have helped :( but she doesn't fuss at the same times every day so I don't think it's colic.  Anyone else been through this?? Any advice??