Is my girlfriend frigid?

My girlfriend is 21 and I am 34 years old. We have been together for 10 months now. We see each other everyday. But dont live together. Recently I have got back into work and I am now in a good job. We use to have sex loads. But in the last 3 months we have only had sex 3 times. She has her own place with a single bed and will not let me sleep over any more, complaining about her back pains. The most I get is peck on the lips now. She won't kiss with tongues because she says its childish. So, quick kiss and a cuddle at her doorway at the end of the day and that is it. She is definitely not cheating on me because I see her everyday, she's not that type and can't be bothered. We say we love each other do which I do to a point. I use to complain about us not been more affectionate all the time which pushed her away. She will not talk about our problem at all! If I even try coming onto her she starts an argument. If I even try talking about sex she tells me to leave and go away. She says I have got to respect her wishes and build up the trust again. I have not cheated on her ever. What she means by trust, i think, is to stop bothering her about sex. She won't finish me. We get along really well. But this sex ban is killing me. I said what about my thoughts and feelings. She said I will take your feelings into consideration when you learn how to respect me and don't bother me or come onto me about sex! So, I have backed off for about a week or two now but nothing has changed which is hard when considering we see each other every day! She is a bit more touchy feely in front of other couples who are friends. But even though we are a drunk she always gets the taxi to drop me off at mine first. What can I do to improve my situation? Any Advice? I'm worried that if I don't show her any attention it will end us completely.