The most helpful job interview I had was when the interviewer broke script and just leveled with me about how I wasn't presenting myself well. There was a shared connection (our alma mater) that must have convinced him to be straight with me instead of hiding how poorly I was doing behind a mask. The HR handbooks say that you should never let a candidate know why they were not selected, but that information can be extremely helpful.
If you're not getting offers, I strongly recommend that you find somebody you trust to do a mock interview. Let them critique your resume, cover letter, posture, awkwardness, lame handshake, etc.