Unfortunately, it sounds like they're trying to push you out. It is probably time to contact an employment attorney and see what they say about the situation, especially with the pregnancy and early maternity leave threats. It sounds like money is tight right now, but if you check online, many states have legal aid services for people who may not be able to afford an attorney. Many attorneys will also give you a free consult to see if you have a case. It sounds like you do to me, but I am not a legal professional. But you are entitled to your ADA accommodations. They are correct, however, in saying that you are still expected to be able to perform the job at the same level as anyone else, just with the extra accommodations.

But to write you up over cleaning a desk? That spells trouble.