MacBook storage filling up automatically

my Macbook pro (mid 2014) has suddenly started taking up 15-20 GBs of storage without no reason.

when i start my laptop it had around 18.7 GB of free storage but as time goes by it automatically fills up storage and now i have only 4 GB of storge left.

sometimes when i restart my mac it will free up all the storage but other time storage is not freed up.

also somethime i have found 'Recovered files' in my trash after i restart the mac.
MacBook storage filling up automatically
 
 
Q