i use bitcoin core. i have 2 transactions from nov 7 that have not confirmed. a few days ago i sent another transaction and bumped my fee up to 0.00012. that transaction has not gone through either. at this point i had 3 transactions that have not gone through. i started to stress and thought something was wrong on my end. i re-installed windows and downloaded the blockchain again. all 3 of those transactions vanished from my transaction history. are those transactions definitely not going through? i hear after so long transactions get dropped/expired/rejected or something like that. however i also hear this is false information and all transactions get confirmed eventually. which is accurate?

i was reading segwit or lightning is suppose to help alleviate the slow confirmations and high fees. is this something that happens automatically or do users have to do something to make it work?

how do i determine what is an appropriate fee to pay?