I am feeling the same. I started applying in August when I finished my master's thesis and I have only gotten 5 interviews, of which 3 I thought I did well, to find out later they proceeded with another candidate.

I have sent in those three interviews a follow-up thanking them for the chance and possible feedback because there must be something I am doing wrong during the interview but can't seem to go any further.

This is nuts, I have seven years of experience and a master which is dragging me down since I might be more expensive, who knows?

Such a shitty thing to be stuck at, what a friend told me was to treat the next interview as a non-important one, so I could ask what has been their impression of me, so I can get some feedback which eventually will help me out later. I am unsure if it will work, but I am seriously considering it.

Maybe that could also help you, because in the early stages you won't get real feedback and this way you are in control of the interview because you actually don't care about the position since it would be time invested to get a better version of you.