My 5 yr old won't sleep at night?

My 5 yr old daughter won't stay in bed at night and I'm at my wits end. She shares a room with her 3 yr old sister but says she doesn't want to be alone. She either gets up and wakes me up, or cries from her bed until I go into her (I can't ignore it or she'll wake her sister up). I'm 8 mnths pregnant, my husband works nights, so i'm on my own with this problem. I'm surviving on 2-3 hrs sleep a night and i just feel like i can't take it anymore. Until recently I would just let her sneak into bed with me but with the baby coming soon have put a stop to that. Now when she gets up I put her back to bed, or send her back on her own, but she just keeps getting up again, or else she'll be as loud as possible. This has been going on for 2 wks now and i need help. I have rewards to give her in the morning if she stays in bad all night, she has managed it a couple of times, only waking once or twice but not being too disruptive so have given her the treat, but the last week she's been getting worse every night. We put them to bed at 7.30, put their bedtime music on and cuddle them to sleep, cuddle the 3 yr old and she ussually nods off within a couple of minutes. My husband cuddled the 5yr old and it ussually takes a good 15 mins to get her to sleep, she keeps talking and refusing to close her eyes. I'm not wondering if there is a child sedative my doctor could prescribe?