You bought that really awful bit, though, didn't you? You can't direct-rein with that. He's probably confused (and having mouth pain).
1. Get his teeth checked and probably floated.
2. Have a professional trainer come out and evaluate him so see if it's a training issue, a pain issue, a tack issue, or a 'you' issue.
3. Look into other, better bits, like the ones you were advised about on your other thread.