Is this burn out? :(

I'm generally used to being one of the top few people in my classes and my GCSE results were pretty good but after coming on to a level it seems I just can't bring myself to care anymore. My homework grades are slipping slightly - not enough for it to be a cause for concern just yet, but I just can't get my self to do as much work anymore. I do have goals and need to achieve top grades to study what I want... And I know I can achieve them if I put the effort in... But I am completely unable to motivate myself the way that I used to in GCSEs and the first few weeks of A Levels - I'm finding getting completely organised hard too - as I can't bring myself to do that either. I'm not finding the work set overly challenging or anything - but as Im leaving homeworks to the last minute so I have to rush them, the workload is feeling a lot greater than it would if I could do it on time. Does anyone else feel a bit overwhelmed like this? Any advice would be appreciated!