how should i prepare for mains in last 5 months, which books should be done regarding the three subjects

In the last 5 month the best way way is to revise and revise with agood amopunt of practise.At least two month before exam join any test series so that you can have confident abot the exam.
BOOKS have to be referred from the beginning
for physics-HCVERMNA+NCERT
CHEMISTRY
PHYSICAL-OPTANDON
INORGANIC=OPTANDON
ORGANIC-ARIHANT PUBLICATION
MATHS-ML KHANNA
I think with apropery strategy prepared by you from the beginning will help you in improving your score