The transition from GCSE to A-Levels is massive, and you will have not been taught how to make that transition efficient. The first few weeks/month will be difficult, however, you will soon develop a routine and make timetables. Then you will be able to balance the work and have extra time on the side to have a life. Don't worry, it gets easier the longer you wait, and many people (including me) experience the hard transition.
In my opinion, the A-Level to University transition is much more steep compared to the GCSE/A-Level one.