Trouble eating/feeding

My baby is a week old & is having problems eating. She will only latch on the right breast but I'm afraid there's not much milk. She rarely will latch on the left & if she does it's just for a few sucks & she's done. She also likes to fight feeding time, she'll suck some then cry..suck some then cry, then after a while she'll latch good & eat for 15-20 minutes before she falls asleep..only on the right side tho. I don't know what to do & it's wearing me out feeding her so often. Also she weighed 5lbs 12oz at the dr 4 days after she was born & she weighed 6lbs 7oz at birth. We go the 14th to re weigh her. I want to keep breast feeding but something's gotta give. Please help!! Any & all advice would be great!