HELP!

Okay so I need help Sesaly doesn't sleep through the night. She will be 3 in just a month and a half. She has never slept through the night well. She will go on spurts and do really well for a couple weeks and then go back to not sleeping. I don't know what to do. She will just join us in bed at night and we will wake up to her in our bed, so I now put the baby gate up in her door at night to keep her in her room, well now she will still wake up and just cry for us. And the baby gate thing doesn't work well for the whole going to the potty at night thing. Why is she waking up at night? I have tried to keep her room warmer that didn't make a difference so I made her room a bit cooler, well still nothing. She is up 2-5 times a night. I really don't know what to do. She even fights naps but if I don't have her take one then she is so tired at the end of the day and usually will fall asleep on the couch.Hadley sleeps better then her! She is only up once and that is at 7:00 am. Please any one I would love advice any would be appreciated.
Thank you!!