Wow- it sounds like your job was available to you, but that you got yourself fired due to your behavior.
Technically, you are "legally" allowed to take medical leave for 6 or 8 weeks postpartum. Whether or not that is paid is entirely dependent on your contract. If you intend to take FMLA, your employer does not need to pay you for the additional time, but must hold your position open. You have to tell your employer ahead of time that you intend to take FMLA and there is paperwork involved. My guess is that you did not do this.
You have no legal rights b/c there's really strong chance that he will say that you were terminated due to your lack of responsibility and insubordinate behavior. Unfortunately, your decision to fall-back on sarcasm rather than waiting until an appropriate (non-alcohol induced) time to discuss your contract probably cost you your job.
You don't say what you do for a living, but I suggest you start working on your resume and start looking for a new job.