You can always improve, you have 5-6 weeks until May, but need to start straight away and put the hours in, there is no easy way. Currently I am working school days 9am-7pm, but make sure I take breaks every couple of hours to make lunch, walk the dog around the block for some air and keep away from my phone during the day as it is too easy to waste time on it. At weekends I fit in 2-3 hours each day in the morning so I get the afternoons and night free, I will do more as we get closer to May. It is only a few weeks but will be worth it, if I need to I take a day off, I also make sure I exercise and get enough sleep as I know I can't concentrate after late nights.
For chemistry and physics I revised all my notes, looked at recorded lessons/youtube/scholar/bbc bitesize or revision books for bits I don't know or if my notes were not clear. Then I have worked through a past paper, marked myself and made a list of areas I need to study. Studied these, then repeat with the next past paper. If you are stuck with something, ask your teacher to help, but try to be specific and show you know most of it there is just one bit you are stuck with. 5-6 weeks you could do at least one paper per subject per week, the first one will be hard as there will be lots you don't know, but as you study it will get easier.
English I find much harder, I practice RUAE past papers and exercises in revision books and mark myself. Also trying mind maps for essay and scottish text and remembering a selection of quotes and what they mean. I don't do geography.
Maybe also think about what your subject priorities are. What are your plans and what subjects do you need for them?