first moms, I need your help

I am feeling very sad about my OA with my son's first mom. She is a great young woman and I care about her very much. but she doesn't answer my phone calls or e-mails. If it were about me, I wouldn't care. but my son is 5 and he really wants to see her, but she hasn't responded to his recent phone call. he is at the age where he is just beginning to understand that his birth mother is related to him and that she gave birth to him. She is VERY busy starting a new business and I don't expect her to drop everything but it would be really nice if she responded to the message. I have a relationship with her mom and in the past her mom has gotten her to respond to me when we were planning a visit (like at Chistmas). What is really striking to me is that when we started our OA I felt overwhelmed with the amount of contact and I needed some space. Well as they say, be careful of what you wish for. I know that I need to give her space and not push things. I realize that contact and visits must be difficult for her. but I just wish she would answer me instead of ignoring my messages. I thought maybe some first moms could give some perspective. When I do see her (first mom) she is lovely to me and to our whole family. I don't know if the lack of contact is because the OA is tough or if she just isn't good at communcating with people. I did see someone on her Facebook page giving her a hard time about not responding to phone calls and messages, so it might not just be me, but I have no way of knowing. By the way, this has been going on for over a year...it takes several messages to her before she responds. I am not badgering her or hounding her. We now only see eahc other a few times a year. The first year or 2 she contacted me frequently and we had visits as often as once a month.