I redesigned my website and lost all SEO rank.
Oh boy, you picked the wrong web designer - we've seen it many times. If you happened to hire a designer with little SEO experience they can fail by changing URLs but not 301 redirecting, removing important content, leaving a noindex meta tag, disallowing on the robots.txt, or not setting the SEO title properly.
Fortunately, not all is lost if you act quickly enough. A good SEO agency can rescue parts of the damage done by identifying and fixing what was missed.