calling all on-call nurses

I don't have a way to advise you to explain it, except as you have just done to us. You don't really have the option to seek additional employment lest it interfere with your ability to take calls. Your employer knows this. You can try negotiating for a better salary, or consider looking for a different position.

In my position as weekend on-call, I am paid a full-time salary for being on call 64 straight hours (Fri 430p-Mon 8a), so it's apples and oranges by way of comparison. I average 35-40 hours worked during that time. Our weeknight on-call (Mon-Thurs 430p-8a) is paid similarly to you, though I'm not privy to the details.

At one point I had a manager try to tell me driving time "didn't really count" for me when it came to consecutive hours in the field (I've been out as long as 20 on a handful of occasions). I reminded her that if travel time counts toward a weekday nurse's hours (it does) it should count toward mine. Even good managers can have blind spots, so it doesn't hurt explaining your case in a respectful manner.