Should I pursue legal action through an employment attorney? I am an associate with 20 years of tenure at a corporation.

I've held 9 different roles and have always had good reviews. In January 2017 my dept underwent a restructure where I felt leadership was setting me up for failure by overloading me with responsibilities and taking away my direct report while they gave my peer 1/3 of the workload and a direct report. I went to HR immediately as I knew this would result in poor evaluations for me. HR deflected my concerns back to leadership who did not change my workload but hired a remote support person. In August 2018 during my evaluation I was told that the workload will not be shifted due to the fact that my peer will not be able to deliver results the same way I would so I reported to HR favoritism, discrimination and retaliation. By the end of 2018 some of the workload had been shifted but the harsh criticism continued which I feel is retaliation since I've been going to HR. During my 2019 evaluation I received a "needs improvement" and I was unfairly written up so I alerted HR that what I had reported in 2017 was coming true. Since 2017 the VP and Director have created a hostile environment which caused me to develop insomnia and anxiety requiring an LOA. What should I do before I return?