Breastfeeding help PLEASE?

My son was born a month early so as he was just a little more weak than a normal newborn, it took him a little bit more for him to feed a full meal from the breast. From day one he knew how to latch on but would only ever do it for 10 seconds or so. The doctor told me to keep working on it and he should start to get a hang of it closer to his due date. He is now one month old and just passed his due date. I kind of have started to use a bottle more than anything as I wanted to make sure he was eating and gaining weight as needed. He still latches on and has even eaten a couple full meals from the breast but now I am ready to get rid of the bottle completely. When it's time to eat I put him to the breast but he gets so frustrated so I calm him down and then back to the breast after we work at it for about 30 minutes I'll give him a bottle :/ I know that's my first mistake. Should I just let him keep crying since I know he know's how to do it OR how should I go about this? Any advice or words of encouragement would be appreciated. Has anyone else went a month and finally got it? I am dedicated to breastfeeding and do not want to give up...........