At first you should check the withdrawal address if it's correct you no need to worry about it. Bittrex is a trusted exchange so don't worry about it anymore. As I know there are something happening and it make Bitcoin trasaction take longer to receive confirm. If you don't want to wait no more longer why don't you try to use Transaction Accelerator on Viabtc
Since my last message from 5 days ago, no more issues for me with Bittrex.
Thanks for the help guys.