My dentist placed biodentine as temporary filling. Days after, it hurts. It's like my tooth will fall. What will I do? Do I need to undergo root canal?

Most likely. These signs may indicate that you have a diseased tooth or infected nerve and therefore may need a root canal. See your dentist ASAP.
Possibly. Your dentist will need to re-evaluate that tooth. May need root canal therapy.
Root Canal. Root canal treatment indicated. Please return to your Dentist or ask for referral to a specialist Endodontists. Sounds like you have an active infection that requires more extensive treatment.