Penalized by google

obviously my site is Penalized by google algorithms. how can I find which algorithm it is? in past 6 month I constantly lost my ranking and even some pages completely vanished from SERP. I tried so hard to figure it out, but still no idea. rewrote my blogs and made new backlinks but nothing changed. I'm still losing my ranking

You can correlate the time it happened with algorithm trackers like this: https://moz.com/google-algorithm-change

You can also analyze your current top competitors to see what is working.

Did you target difficult keyword, what kind of backlinks are we talking about and instead of chasing updates, target easy keywords, strong links to get your rankings back