I was fired then rehired a week later because they didn't know I had a health condition. my boss after rehiring me asked me to show him proof that I had the medical condition. is this legal ?
There really isn't enough information here to fully answer your question. Yes, your employer should engage with you through an interactive process to try and work with your medical condition. Your end of this particular bargain would be to inform your employer of nature and extent of your condition. This could include a communication from your treatment provider.
There may be more at play here, there often is. I may encourage you to speak with an attorney to make certain you understand your rights. Prior to speaking with an attorney I would recommend your review http://www.hum.wa.gov/
Best of luck.
It is difficult to answer your question here. Certainly, your employer can hire and/or fire you for any non-discriminatory reason. It seems, based on your facts, that you do not allege that they fired you initially due to any knowledge of your health condition, but rather, that, after getting wind of your health condition somehow, they then opted to return you to work. If this is true, then I don't necessarily see any claim or why you would want to pursue one, since you have the job.
With respect to the request for your medical condition, again, it is tough to answer. Are they asking for this information as part of an attempt to accommodate your disability? If so, they are entitled to some information regarding your disability and the accommodations needed.
This answer does not constitute legal advice and you should contact an attorney to confirm or research further any statements made in this answer. Any statements of fact or law I have made in this answer pertain solely to New York State and should not be relied upon in any way in any other jurisdiction. Additionally, we also encourage you to reach out to us via Twitter (https://twitter.com/#!/employattorney) or Facebook (http://www.facebook.com/WhiteRicottaandMarks) if you have follow up questions as we do not monitor questions after providing an initial answer.