Okay, so you have tried bittrex, that's a good way to buy more steem, can be a little daunting if your new to crypto.
I always tell people if you want to buy more steem.
Buy some Bitcoin on Local Bitcoins.com and the send to bittrex or Poloniex, but Poloniex has been unstable of late.
Trade Bitcoin to steem
Then send your steem to steemit.com and then power up!
Let me know if this helped