Need help

I’m not getting a lot of hours at my current job and i want to go back to my old job. They said they can do Thursday-Saturday 24 hours a week but I talked to my boss and she said she’s going to post a full time position a couple weeks ago but it’s still not posted. I’m planning on going on leave the beginning of June and my old job said I can start in March and probabtion period is 3 months. I currently work in a hospital on call and have 16 hours on this next check and I really don’t know what to do.