FMLA and overtime

I have a chronic medical condition and have been approved for intermittent FMLA. Last I utilized three days of FMLA; my employer was shorthanded for the weekend and I agree to work two shifts. There were no agreements made beforehand, and I've now been informed that I cannot claim overtime for those hours and that I will still be docked 8 hours wages for the week AND be charged with using three FMLA days.

So, I have two questions. Is FMLA considered time accounted for during the standard work week? Such that, if x=FMLA hours used and y=actual time worked, then if x+y > 40, then is anything over that limit eligible for overtime pay?

As well, if I work a standard 40 hour week, can my employer charge me a number of days of FMLA to exceed that number? Can I be charged three days of FMLA when I worked 32 hours?