You will need to see an attorney who can sit down with you and go through the facts in detail. What you will need to show is that the reason your employer is putting forth for firing you is what lawyers call "pretext," that is, your employer is making up a reason for firing you when what it really fired you because you are pregnant. Just based on what you shared here, it sounds like pregnancy discrimination is your best angle. For the federal pregnancy discrimination act to apply, your employer must have at least 15 employees. See www.eeoc.gov. If it has less, you can still file with the Alexandria Office of Human Rights, but not for money damages. I suggest Avvo or www.mela.org to find an attorney who can speak to you about your case. Sorry to hear that this is happening to you. Unfortunately, it is all too common. I wish you the best of luck
Note that this is not legal advice and this does not establish an attorney client relationship. You should review your issue with an attorney for the best possible answer to your question.
You have presented a number of facts, which may or may not be related to your pregnancy. Some of the information is difficult to follow because we don't really know when the events occurred in relation to your pregnancy. You really should discuss your matter with a local employment attorney, who can advise you after hearing all of the facts. Good luck.
As another attorney has already said, your employer nitpicking on you for every slight, might be a pre-text for discrimination; did the store manager engage in the behavior prior to your pregnancy? If no, you might have a claim for discrimination. You can contact my office if you want to discuss this some more.