Is chemistry a subject you havent already taken? Chemistry is definitely not an easy subject and many people I've come across have said chemistry is harder than maths. As for maths, first year maths is easy- a lot of people will agree on me with this. Second year maths is where it gets rocky, that said, there are loads of great YouTubers to teach you. You would definitely have to get into the habit of revising daily though- studying chemistry and maths together may well impact your psychology grade if you're finding the 2 taking more of your time away from psychology.