I think my SO mom hates me....

Nothing is wrong with my relationship in my eyes, I'm personally very happy with the guy I'm with and I hope that he'll be the one I marry one day. We're very sexually active and support one another and are great with giving each other feedback. We spend our nights playing video games and I shit you not lighting our farts on fire, laughing and joking around all the time. I live with him and we aren't overly attached.. he'll go out to the garage and spend time working on his car cause we both know if we're together too much we'll begin to fight. He's really showing me how to live in this world too, how to grow up and take care of things myself.. My problem is his mom. She seems to hate me.. His dad takes on my side when she gets on to me for nothing and she DOES NOT like that. I'll be sitting next to my SO in the living room on the couch and I'll look over and she'll be glaring at me for some odd reason. My SO says it's just pms, but I've noticed this ALOT lately in the past couple of months. It worries me because I don't wanna be the cause of family problems in his household and it makes me wanna move out tbh. I just have nowhere to go right now, other than my grandma's and I don't want this to affect our relationship because I know it will. He's already stood up to his mom once for me but I don't want this to get worse. I just want her to like me. Opinions? HELPPP..