My weight loss goal is 90 pounds. I'm

Forfet that. You should gain 90lbs.

See
https://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmicalc.htm

That is far too light you will have to damage your muscles and health to be only 90 pounds.
You should change your goal to be between 122 to 164 pounds which is the weight a healthy BMI would be!

Think healthy is beautiful,
because skin and bones and malnourished certainly is ugly.

I'm 5'9" and I think my last ** weighed 90 lbs.

no u wont you'll want to be 80 then less then that trust me i've been down that road it never ends...please seek help

to be 90 lbs or to lose 90 lbs? That is a big difference.