Don't know what to do

I have just started A level studies this September and find myself in an odd and confusing situation.
Firstly, I'm doing biology, chemistry and sociology and at gcse I got an A in both biology and chemistry. Now studying those subjects I find my self doing quite badly at class tests. For example I got D D E in my biology so far and a D in my chemistry.
I know the content, I'm sure of it. I would like some suggestions as to what I can do about this or if this is normal at my stage. Thanks to the new spec I can't really find many past papers to practice from because I think it is my exam technique.

It can happen when you're not used to the style of questions. I had a similar situation when I started GCSEs in year 10, I got D's and E's in all my first tests and then came out with A*s in almost everything at the end of year 11, it just takes practise getting used to the questions and how to answer them, and this does come with time. So don't be disheartened, get motivated by it and aim to do better before the real exams! I doubt the exam questions from previous years are much different though, so still do past papers, and ask your teachers to go through what you're doing wrong in these papers (and if they won't, then you could even show me and I'll tell you instead!).

Just something else I want to add, if you go through your paper, then you'll be able to find out whether it is actually your exam technique or whether you don't truly understand the content, because sometimes you might think you know stuff until you have to actually apply it. The reason I say this is because exam technique plays quite a small part in bio and chem, when I got all my D's and E's, they were in things like history and geography (where answer technique is much more important), so I'm just saying, you might want to check if it is actually your exam techniqe that is wrong