USPS Emoplyee Terminated Prior to 90 Day Probation. Worked less than 40 hrs a week.

I was hired by USPS on April 27 as a Mail Handler Assistant and "released" on June 29 on midnight. I was taken to the backroom and told I was fired after an evaluation where they rushed the meeting and simply had me sign the few papers before actually giving a reason for my termination. I was told that I was let go due to being slow during work despite being just as fast, if not faster, than my coworkers. I had completed every task I was given, I have arrived on work on time, and there were no complaints about my behavior. Still, despite this, I was let go and told not to re-apply to that location. I was given an evaluation a few weeks prior, but I was never told how I should be improving (largely because there was nothing to improve). There was no notice, there was no procedure - it was a rush job with me ordered to turn in my badge and time card.

Also I had brought to my supervisor's attention that for a few weeks, despite working over forty hours and being present even when sick, I was being underpaid for less than forty hours. However, he only gave me the records of the weeks instead of actually assisting me.

Is there anything I can do about this as I am sure this would affect my obtainment and applying of unemployment checks and I believe this was a wrongful termination.