Boss won't give me day shift

My boss won't put me on day shift bc im a supervisor and she "needs me on nights right now" but her and the other supervisor are on days and someone who has way less seniority than me just got put on days (I'm a law enforcement dispatcher and I work 4 tens and get off at midnight ). I can usually get caught up on sleep on my days off but on the nights I work it's really hard bc my son gets his best sleep while I'm at work, then by the time I get home I'm lucky if he stays asleep until about 3 am and then he's up every 2 to 3 hrs like clock work after that and so I end up with severely broken sleep on the nights I go to work. I also slept really poorly the whole time I was pregnant and on up until now. Occasionally I'll get home from work amd he'll sleep til like 5 am or 5.30 but that is the exception not the rule. I feel like I'm dying and bipolar bc of this. When I have sleep everything is fine including work, when I don't have sleep I cry, yell, basically can't handle life...I even cry at home with the baby sometimes when hes awake early in the am on days i have to work bc I just wish he'd go to sleep so I can sleep too...my husband thinks that I just want him to sleep all the time but that's not it, I just can't handle this broken sleep, it's killing me...making matters worse is that I'm training a new dispatcher at work too and that's extremely stressful in itself...I would demote if I could afford it to claim my seniority regarding day shift but I really can't give up the extra money....any ideas???????