It's possible that those unconfirmed transactions are only on your local node and hasn't been broadcast through other nodes.
Try to open your wallet with
-zapwallettxes command. It may solve the problem. The command makes bitcoin core forget about unconfirmed transactions on your local node.
To do so, open your wallet using the command below in cmd.exe
"C:\Program Files (x86)\Bitcoin\bitcoin-qt" --zapwallettxes=1
You can also export your private keys and import them into other wallets like Electrum.
Following topics may be helpful to you.
cancel old transaction / update my blockchain?Can't send because of "txn-mempool-conflict"