Cat losing weight.

My cat is only about 2 years, she is female. She recently got sick, she started off with a high temperature and not eating or drinking water. So we took her to the vet and he gave her antibiotics and about 2days later the vet told us we could pick her up because her temperature was down again.
Anyways she was fine after that and we thought she was better then this has happened all over again and its happened now countless times in the last few weeks, back and forth to the vet(3 weeks or so) and he keeps just giving her antibiotics. She is eating a bit now but she can barely walk. Its like her legs have become lame. She is all wobbly and she just falls over sometimes. She just sleeps all day and night and sometimes gets up to go to her sand box but she wont even go outside because she is too sore to get through the cat flap.
She has lost so much weight. Also when she tries to jump onto the couch or bed her claws get stuck and she cannot seem to retract them. Any idea's what could be wrong with her. Any home remedies? I'm afraid we might have to put her down. :( She is getting worse