the way you have worded your post has raised red flags here.

90ºF is being measured where? is this an ambient air temp? a surface temp or? Ideally the tank will have two of the same hides under one should be about 90º (with in 2 degrees) The under the other hide should be 80º (with in 2º) The air inside the tank can be between 77-85 or so. This is ideal. It is unclear from you post what or where your 90º temp is if it is under the hot side hide this is good.

A shed cycle usually takes about 10-15 days after complete it is a good shed (all off the shed is off the snake and is ideally in large pieces or a single continuous piece.) or a bad or incomplete shed. This is a shed where chunks remain on the snake. In this case either correcting the RH issues and providing a humid area can help or even a soaking in water that is between 82-88º the water should not be deeper than half the width of the body of the snake (typically for a small snake only an inch deep or so)

Again you have worded things that sounds like the animal COULD be severely dehydrated as well. Has the snake been eating regularly? This answers most of the husbandry questions. Dehydration can be treated with soakings daily for about 20 min each (dry the snake before returning it) for a week or so. This is beneficial if the animal does not become very stressed by this process. Discontinue if it is stressed. Correcting the RH to 50-% will solve shed and hydration issues.