Why is my phone on a boot loop?

So recently my phone was having issues where it would turn off constantly for 4-5 minutes at a time even when charger was connected and for some reason it couldn’t hold a charge so I was thinking this was caused by a battery and ordered one on I fix it then replaced it my self everything seem okay but felt a little sluggish so I let it charge for 2h to see if that changes anything but not sure why but the battery was at 46 then jumped down to 3 then 1 from a matter of 10mins so after that I knew a guy that works on phones then he connected a new battery and seem to charge perfectly fine then changed to the ifixit battery and that also seemed good until I dropped it on accident and the phone goes on a boot loop until it dies the next day not sure what to do btw I got a new battery and got the same problem can someone help me out