I've been in that situation a few times. It always seems to be the hardest of workers in some companies that get picked on. It's not you so much as the employer. I know so many people who have had horrible employers that would look for the smallest fault to get them fired. But it's really not you. They way I looked at being fired was a chance to move on to greener pastures. I think I even went back to my old work and thanked them for firing me. Ooooo, the look they gave me. Eh, just shows how miserable they are stuck stocking junk at a cheap dollar store. I then called Health and Safety Inspectors to alert them of the hazardous conditions they kept their store in. Karma.
Hang in there. Everything will be okay.