Keep Trying.

Informal stats I've seen say that the big players still reject 80% of their onsite candidates - you're not a loser, it happens to a lot of people.

I failed 3 in a row in one week once - not fun. I know how you feel. I was pretty bummed for a few months and it took me a while to restore my confidence.

For me, my progression with tech interviews was definitely non-linear. I sucked at them and felt terrible and incompetent, and then suddenly things started to click very quickly and I'm alright at them now. The only real way to get better is practice.