Is this ridiculous or what?

My mother is really over bearing. I'm 19, and my boyfriend lives an hour away. When he comes to visit once a week (oh yeah, my mother won't let me go to his house because he lives on his own), we always end up cuddling on the couch and watching a movie til midnight. My mother doesn't like that, so the lights have to be on, and my dad has to be in the next room (spare, he sleeps down there a lot because it's less stuffy than the room upstairs.) Well, today I kept turning off our air conditioning (mum...it was set at 17 C) but she wanted it on. I put on a sweater and got under some blankets on the couch and watched a movie. Well! If that didn't start a fight! My mother thinks my boyfriend and I are "doing it" UNDER THE BLANKET. WITH MY SISTER AND FATHER IN THE ROOM. My mom has no reason to ever doubt me. I've never gone farther than kissing, and he was my first kiss. We've been dating a year. She won't let us do anything. She's always like, "That's inappropriate" (when I kissed him after not seeing him for three weeks). "You have to wear jeans, not shorts. They're too short and he might.."(What, he's going to finger me as I'm walking? Sounds...difficult...and how...?? Never mind..) She doesn't trust me one bit, even though she has every reason to. I've never given her any reason not to trust me, and it's annoying. She treats me as if I'm a drunken harlot who sleeps around and got knocked up, even though I'm the exact opposite. What should I do? I've tried telling her that I'm not doing anything, but we always end up fighting. HELP!