Give us the following information. The more you tell us, the better we will be able to help you.
What has the bird been eating and drinking, if at all.
Describe the housing/bedding in use.
Temp at 90, is there also an area away from the direct heat source?
Are there more chicks in with this one?
If so, do they huddle together (as in cold), or possibly try to get away from the direct heat source (as in too warm)?
Any other info you can think of will be helpful.