Having troubles

I don't understand she's my third baby. My first I breastfeed for 9 weeks and gave up, my second I breastfeed till she was 17 1/2 months, it was so easy and I loved breastfeeding. With my third I tell myself everyday not to give up its now been 6 months I still feel the same. I feel like I can't do anything she screams here and there at the breast and fights her naps and going to bed. I'm emotionally drained at this point but I don't want to give up. She's gaining weight perfectly the drs have no worries. I'm just over stressed and have no one to talk to.