How To get Ex back when theres a child involved?

I have a 10 month old son. His mom and i were together for almost 2 years when we found out she was pregnant. When or son was around 3-4 months we broke up. The months after that few very chaotic, lots of argueing, and yelling. She was only 20 years old when she had him, and is now 21, I was 26 and now 27. The last few months our relationship has been on the good side. We hang out regular. At times we get along like we use too. Our conversations would be pretty detailed about whats going on in our lifes, then she can turn a 180 and totaly block me out of her life and not have any interests. I still have feelings for her and at times i know she does for me as well. It seams that whenever she goes out with friends, we always heads for a few days. Her attitude changes and she is rude and distant. What can I do to get her interested in me again relationship wise?