Mother-in-law

***DISCLAIMER*** Sorry this is such a long post but I just really have a lot I want to get off my chest. 

My mother-in-law hates me. Well, it's not that she hates me really, it's just that she wants absolutely Nothing to do with me, my husband, or her soon to be grandson and I have no idea why. My husband is the baby and the only boy so he's always been her favorite according to his sisters but ever since we got married it's like she doesn't even care about him anymore. He is in the army and over seas and before he left she stopped talking to us because we didn't go and see her on Christmas. All day Christmas eve and Christmas Day I reminded my husband to call her and ask when we should come over but he waited until 10 pm on Christmas Day before he ever even called. It was his fault we didn't see her but she still blamed me and even unfriended me on Facebook because of it. Like I said, he was going over seas after the new year so we wanted to see her before then so that we could tell her that I was pregnant but she wouldn't answer any of our calls or texts. We even tried going to her house but she just ignored us and wouldn't come to the door. Eventually he left for his tour and I got fed up with it so I told his sister to tell her the good news since I couldn't get in touch with her myself. After his mom found out I was pregnant she friended me on Facebook and sent me a message saying that she's happy and she hopes that it's a boy. In this conversation I decided to ask her why she was mad at me and why she didn't like me. Her only response to this was, "this isn't about you, this is between me and my son" which is weird considering the fact that she only unfriended me and not her son. Everything was ok after this, I updated her on the pregnancy and sent her sonogram pictures and she would message me and ask me how I was doing, she even started talking to my husband again. For some reason though, that all changed changed after I sent her an invitation to my gender reveal party. The party was kind of last minute and I made the invites myself so I didn't have time to mail them, I just sent them to everyone electronically. I sent hers via Facebook and noticed that she saw it but didn't say anything. My husband assured me that everything was ok and maybe she just didn't have time to respond yet so I didn't really worry about it. The day of the party came and she still hadn't said anything but I assumed that she would be there anyway. Well, I was wrong. Both of his sisters were there but his mom was not. When I got the chance I pulled his sister aside and asked her if their mom was mad at me or something. She said, "oh no, she wanted to come but she just had to work". This made me feel a lot better but then, Mother's Day happened. When it got close to Mother's Day my husband sent me some money to buy both his and my mom some gifts. He told me what his mom liked so I picked the gifts out and sent them to her along with a heartfelt note from her son. On the day of Mother's Day I reminded my husband to call her and I myself sent her a message wishing her happy Mother's Day but neither of us got a response. My husband tried calling her all day with no luck. I talked to his sister and she told me that his mother got the gifts but didn't say anything about them. After that, she unfriended both me and my husband on Facebook and made it to where we can't send her a friend request. I honestly don't know what her problem is and I don't know what to do. We are having a son in August and I want him to know who his grandmother is and I don't want him to feel like it's his fault that she doesn't want anything to do with us. I'd love to say that I'm over it and that it doesn't bother me anymore but the truth is, it really does bother me and it probably always will. All of my friends have such good relationships with their MILs and I just want the same thing.