I was in a very similar position as you a while ago and was equally despondent. I thought I was a good engineer, I had a good track record and experience, lots of open source, etc but my interviews were a dice roll. I would either answer the question easily or fumble quite a bit and not get the offer. I would get extremely nervous during these high pressure interviews and the more I was rejected the more nervous I got.
My saving grace was finding a place that didn't haze the shit out of with whiteboard coding but gave me a very involved take home project solving stuff similar to their real world problems (I did do a timed online coding screen and some high level technical discussions as well). Obviously there are some downsides to doing a take home project in terms of the time investment, but see if you can find a more enlightened place that gives you this option. Maybe someone on HN knows of companies who are open to this.
My saving grace was finding a place that didn't haze the shit out of with whiteboard coding but gave me a very involved take home project solving stuff similar to their real world problems (I did do a timed online coding screen and some high level technical discussions as well). Obviously there are some downsides to doing a take home project in terms of the time investment, but see if you can find a more enlightened place that gives you this option. Maybe someone on HN knows of companies who are open to this.