If this was happening to me I would start documenting everything right away.
I would write down the date and time I was called into the office and the names of the supervisors and the comments they made, and how I responded, and how their comments made me feel. I would include the date I am writing down what happened, like keeping a diary.
In this "diary" I would include every remark, especially ones like "Why won't you get back on the pump?," comments about a food you consumed, and questions about free medical supplies.
If I could not remember exactly what someone said, I would write "_____ (name) said something like....," or "to the effect of..."
I would include any action that I felt was unfair, for example, "Today, at about 2 p.m., I was told by ____ that I was working too slowly for only folding 5 shirts in 5 minutes, while I saw that another employee, John, got no scolding for folding 4 shirts in the same amount of time."
At the end of each day I worked, I would document, to my best recollection, how many times during each shift I had to step away from the register to check my bg. I would document it if anyone stared at me or looked at me like they were cross at me, or rolled their eyes at me upon my return.
When keeping this documentation, I would remember that someday it may need to be shared with others, so I would keep it on subject, detailed, yet to the point, (I wouldn't write that my cat just threw-up in my shoe, or that my boyfriend gave me a rose today), and not doodle in the margins or express myself in curse-words or sloppy language and avoid miss-spellings.
I would never take my "diary" to work with me lest it accidentally fall into the wrong hands.
I would keep any written warnings or possibly important papers that my employer might give me.
When at work, I absolutely would not, let me repeat that, absolutely would not threaten them with any legal sort of action, or mention or try to explain my legal rights to them. I would be very, very careful o