Shift Diffs, Weekend Diffs??

We would hate to see our overtime pay go. I live in Michigan and work as an ACNP in the ICU. We are employed by the hospital and are the only NP's who rotate shifts and work on weekends and holidays. Basically, we work 3 12-hour shifts per week but get paid for a 40-hour week (meaning we get paid for an extra 4 hours we didn't work each week). We get paid overtime (a set hourly rate, not necessarily time and a half of hourly pay) for any hours worked above the 3 12-hour shift we are obligated each week. If there is an approved holiday during a specific week, we are to take 8 hours off work that week but if we choose not to do that, we get an extra 8 hours of overtime pay. Off-shift differentials and weekend differentials are 10% of the hourly pay. Off shift is any hours worked after 2 PM.