Breastfeeding rant..

My daughter is 3 weeks old, I started out just breastfeeding, and since the beginning it just wasnt easy for me. At first i didnt think she was latching correctly & i never heard or seen her swallow or anything, so i saw a LC. And she assured me the latch was fine.. But she wasnt gaining good weight but she was wetting and dirtying diapers like crazy. Since she isnt gaining like they want her to (she was 6lbs 11oz last appt her birth weight was 6 12 she gained 3 oz in 5 days and they said they want to see her gain a oz a day) they have me supplementing. And when i give her a bottle (half breast milk half formula) shes content after but when i feed her from my breast she isnt and always wants more even though i can feel that she emptied me?! So i really dont get it.. Everyone else says they just stuck their baby on there boob for 10 mins and they were done and they were chubby and happy. Not my case! Any tips??? I hear it gets easier