That happened to me a few years ago. I was having a rough time at school, my time was limited, my parents were nagging me to practise blah blah... I got to absolutely hate the piano, and anything to do with it. I insisted on giving up after Grade 2, and after trying to persuade me they eventually let me.
I didn't touch a piano after that for... oh, about three weeks. Because, stopping lessons gives you this amazing feeling of freedom, when you realise you don't HAVE to play the thing, nobody's making you do it any more. It makes music something you play for fun, instead of something you're expected to do because you've always done it and your family are paying for it. That's why, pretty soon, you feel like playing again

So, instead of doing lessons for a bit, I just took it easy and learned some new pieces. And then when I had to do Grade 5 a few years later because my sixth form required it, I got into it happily again because I was doing it for ME. We all get sick of music sometimes, but don't give up! Or at least, not totally.
xx