3mth old BFding dilemna

Last couple days in the evening my daughter has been doing lots of "gumming" my nipple, latching on/off, favoring left side more...straightening back, pushing away from breast and small cries with her feedings. Dr did say she sounds colicky at night. I went back to work last week, not sure if this could be part of the reason why. Any tips on getting her to stay happy and latch on? I worry about my milk output going down because of this, should I be?!