I think my boyfriend's sister doesn't like me...

I don't know what to do. I think my boyfriend's sister doesn't like me. She's done some kinda rude things nothing crazy but still stuff that rubs me the wrong way. (Maybe it's just a difference in personalities and she doesn't mean it.) But my boyfriend is military so he hasn't been around in like 3 months. I've gotten pretty close with their mom but I also noticed a shift in her. When I'm at their house their mom is great but if she is also at the house I feel like I'm not wanted. Idk. I want to ask him if I've done something that he knows of or if he has any advice on how I can grow closer with his sister but I also don't want him to feel like I'm making him pick sides. Any advice ladies?