Waiting to Transfer Position

I started on my unit working straight nights because it was the only position available. 3 RNs then quit in December, so I applied for a day\evening position on my same unit (all 3 were day\eves). HR called me before Christmas to tell me I got it and I accepted the position that day. They told me my manager would contact me with details for a start date, but he never did.

We're scheduled 4 weeks at a time and I watched one go by before I sent an email to my manager. He told me that I'd probably start the end of February. They posted the schedule for February and I was still on straight nights. So I asked again in the end of January, and they said maybe for the last half of the next schedule, or we can flex you and give you some day shifts. Nothing actually ended up happening.

I asked them again the last week of February and they explained they were moving everyone into the positions in order of seniority. I'm third to move which puts at the schedule for April/May. Well they already have a preliminary work-up of that schedule out and I'm still on straight nights (this will make it almost 5 months since I accepted the position). I emailed my boss about it because I also noticed they'd moved a nurse with less seniority than me to her new position off straight nights (another job opened up on our floor after the 3 earlier postings; we're union too).

He wants me to page him next week when I'm working so we can discuss it. I'm trying not to be bothersome, because I love my job and I love my floor. I just don't love the night shift. It screws my body up so bad that I'm exhausted and sick for almost all of my days off. I don't really know how to say this to my boss, but my health has suffered greatly since taking the straight night position.

I only ask once a month what's going and when they think they can move me. Am I being too bothersome or is it in my right to keep checking the preliminary schedules and asking them about it? And how do I explain how hard working nights is on my body without sounding like a baby? I've been sick more times since working nights than I ever was before.