Hlo aspirant,

First of all you need not be stressed , because stress reduces our efficiency of thinking and remembering . For this you should regularly do some yoga or just go for a walk . All I want to say is spare some time for yourself and it will definitely help you recover from your stress .Now coming to your question , it might be due to the reason you are not interested in medical or for some other reasons , which you have to figure out by your own ... here are some ways which will definitely help you remember things ....firstly , try making small notes and paste them on your notes , secondly make a paper of formulas or short notes and paste it somewhere in  room from where it is visible to you .....because when we see things regularly , we automatically remember them ... this is a fact..... try learning short tricks either by watching some videos on you tube or by some other means. revise the things regularly , and learn derivations by writing then and practicing them again and again .....

Hope this answer helps you....

Thanks a lot and All the very best!