Do I need better friends?

I been friends with these two girls for a while. The first one lets call her sandra, had been my best friend since we were in middle school. She often ditched me for other people but since I had other friends I never seemed to mind or care. Anyways the second one lets call her ginny I have known since elementary but we went to different middle schools and reunited in high school. Ginny and I were just cool with each other never much best friends until now. Well we all started hanging out a lot just the three of us since january and it started with just a casual hang out between the three then we started hanging out all the time on weekends and weekdays. Sandra and I were always closer since we had been best friends longer but now I feel that she doesnt want to be my friend because we have a three way message on facebook and she always asks about ginny, or last time when I told her we should go shopping she was all ok but lets not tell ginny cause I feel bad. which is weird since we never had that problem. I just had a birthday party last saturday and at my birthday party they were all talking and stuff which was fine I had the rest of my friends to talk to but then we took pictures and they were all hugging each other and talking and were kinda ignoring me. I had to go to the club that day and needed ginny to go with my other friend so she could get dropped off at her house and I could make it in time, but she was all NO! i cant my mom is gonna now(which is a lie cause I dropped her off at her house and it was so dark her mom wouldnt of even be able to tell plus this girl is TWENTY!) anyways then sandra is like NO ginny you are going with us! which annoyed me cause they knew I wasnt gonna make it unless Ginny went home with my other friend. Sandras home is on the way to mine so it was ok that I take her. either way I am sick of it, I didnt make it in time for the club and my birthday celebration kinda sucked. both of them usually throw tantrums when I cant do something like once Sandra wanted me to pick ginny up but I didnt have gas in my car and she was all PLEASE PLEASE! I was like I seriously cant I have no money or gas. Sandra has two kids and is 19 and Ginny is 19 single no kids but her parents are super protective even though they have no reason to be. and neither of them can go to the club which is why I needed to drop them off.