As of right now, I do not see a legal claim. I agree with the above posting, you should try to get a doctor's note and see if you can take a few days off to hope this dies down. Your employer only cares about getting the work done.
An employer cannot discriminate based upon pregnancy. However, if she cannot perform the essential functions of the job, the employer may have options. I suggest you consult with an attorney to discuss in more detail and go over all of your options.
It can sometimes be difficult to determine the "real reason." If you suspect your termination is discriminatory, I suggest you consult with a local attorney in order to go over the details and determine if you have a claim.
More information is needed to properly answer you question. If they are offering money as part of the severance agreement, you may not be able to qualify for unemployment. If they are not offering money, you should, but there is no reason to sign the agreement. I suggest you consult with an experienced employment attorney before signing the severance agreement.
Absent a contract of union agreement, you are an employee at will and can be fired for most reasons. They are not required to negotiate any severance with you, though many companies do. I suggest you consult with an experienced employment attorney to go over your options. Good luck.
You should consult with an employment attorney soon. Are they not paying you at all for your commissions, or some reduced rate. If they are not paying you at all, you have a claim for that money, as you have earned it. If they are paying you some reduced rate, you still may have a claim depending on your agreement. As noted above, they can change the terms of your agreement, but not after the commissions have been earned.