There are various laws prohibiting pregnancy based discrimination. The comments made by your general manager seem inappropriate. In addition, if you are being held to a different standard by being required to provide more medical documentation than employees absent for non-pregnancy related reasons that would also suggest illegal discrimination. You should speak with an employment attorney as each case is fact specific. I would be pleased to discuss your situation with you. My number is 860-216-1965.
Licensed in CT and FL
It is not unusual for an employer to ask that medical documentation be provided to determine what type of accommodation should be provided to you. However, it should not be used as a basis to terminate you unless you have been in breach of the terms and conditions. The comments were totally inappropriate and shows a need for training. Depending on the number of employees, file a complaint with your local state Human Right Rights Commission and/or simultaneously with the EEOC. If the employer continues their discriminatory practices and starts retaliating against you for making a complaint or the environment gets worst contact an attorney immediately.
This answer is predicated on the facts provided in which the lawyer cannot confirm or verify. I do not represent you as we do not have an attorney-client relationship.