Completely possible, although it's more likely the result will be in the region of A*AA to A*A*A if you work hard starting right now.
Working hard means being completely motivated, not just learning the basic requirements of a course specification and past papers, but actually understanding everything and doing extra questions out of textbooks. You need to be proactive with your learning style, especially with Chemistry - draw all the chemical reactions and tests out and their relationships. For History, you'll need to look at the past papers and look at the style of questions/dates they relate to and memorise every event for the main topics in chronological order to be able to justify each point you make in an essay.
You'll need to be strict with yourself, which means a timetable from getting home/what to do each day in your frees/ targets for each week for each subject. After each topic, a good way of testing your knowledge is to close your book and recite from memory what you just learnt.
This is what I did for two months straight during study leave. I did the sciences (Maths, Biology, History, Chemistry) which I daresay involves more work then your current subjects, and our biology module had no textbook so I wrote my own using other textbooks, detailed diagrams for every process, supplemented by questions asked in papers and the mark schemes to get the 'key words' they always look for. I studied math until I could do every single question in the textbook without getting stuck, and then moved onto past papers - which I couldn't do at first. In the end I got an A*A*A*A and in my first year, I was like you with my AS results.
It is hard work, but you just need to grit your teeth and do it, for these few months if you make it your only priority, it will definitely be worth it. Make sure you are harsh with yourself when marking and testing, getting an A* is more about knowing every single small detail and WHY, than simply just knowing your course. I would suggest you make your notes that you'll revise from (they need to be at the level where you don't need to refer to any other source) for the next two months - and especially re: chemistry, you should also make sure you re-learn your AS content as well. After this, you should do all the past papers, and add to your notes with exam questions. And then repeat, learning your notes again. 4 months is an incredibly long time, and there is absolutely no reason for you not to be able to get a minimum of AAA if you actually use all the time productively.
Think of it this way - it's just 4 months of your life to swap for those 3 letters on that paper, which will stay with you for the rest of your life. Are you really going to let your procrastination over useless things close doors for your future?
Best of luck.