Need some advice please

I'm 20 years old, as well as my girlfriend. We are both lesbians. I've been with her for a year and two months. I've met her parents many times, but I'm having trouble believe her mom likes me. Her mother treats me very well. She is nice to me when I go and visit. I try and be polite, and conversate with her, but I'm not that talkative, and a shy person at times. Especially with her parents. However I try not to be. Recently, I've noticed that her mother treats me differently then the way she treats my girlfriends older sisters boyfriend. She'll hug him and talk to him and does anything for him. When I am there, she rarely talks to me. I know it's a two way street and I should talk to her as well, but it's hard for me to open up to someone else with out them doing the same. My birthday passed in April. I was hopeful that her mother would wish me a happy birthday, childish I know but I just wanted to know if she likes me enough to maybe wish me a happy birthday. She did not. A few days after my birthday, I visited my girlfriend, still no birthday wish no conversation no "so how was your birthday?" Nothing. My girlfriends sisters boyfriend, got a hoodie from the mother. It crushed me. Not because I didn't get a gift, but because she wished him a happy birthday. I truly felt like I wasn't part of the family at all. When I go over, I try and help around the house as much as I can, as I sometimes spend the night. I rarely get any thank you'd for my effort. Small gratitude would make me happy, because knowing I made the love of my life's mom happy would mean everything to me. My girlfriend spent a week with me, while her parents remodled their kitchen. Her mother had posted a comment on his Facebook thanking him and my girlfriends sister for helping them, and that she loved them both. It made me very upset. I'm not trying to be selfish, I just want to be loved by my girlfriends mother the same way she loves him. I know I can't force it, so I have no idea why it's hurting me so much. But I just don't know what to do. I just feel out of place at her mom. It's to the point where it's depressing me. And I feel like this is childish of me. I just need some advice. I talked to my girlfriend about it, she was furious that I felt this way because her parents are nice and good to me. I understand her anger, but I'm not sure she understands why I feel this way.

I understand what you say. Well I am not sure where do you live but where I live your life style is completely accepting and welcoming. well there is something you should understand. Some times it is hard for parents. As a mother I like also to see my daughter getting married having children. I don;t think that she is doing it express. Some times it is logical mother attract to guys mean future son in laws. what most important for you how your girl friend treats you. If she also treats you different then it is something. Just ignore them for a while. And don't expect any special kind from them, I know easy to say that getting it done but what I say don't worry. And don't let this become an issue between yo two...