Toddlers poor sleeping

Desperately look for advice. I have an almost 2 year old son. His dad and I have separated although they still have regular contact. Anyway so it’s just my son and I at home. Lately, he’s been going through a terrible stage of waking in the night or even in the evening around 8/9pm ish, sometimes later etc and he just stays awake. Wouldn’t be so bad however, he also gets up between 4/5am, regardless of how he’s slept in the night. I’m pulling my hair out. I’ve started to dread nighttime’s. We used to co-sleep and still do on and off however I am making efforts to try and keep him in his own bed. When he is waking in the night I go into his room and stay there next to his bed with his hands in my mouth (that’s his comfort, hands in the mouth). We could be laying like that for an hour or so, I’ll be falling asleep but when I look at him he’s wide awake. I’m finding this so frustrating and hard to deal with as im pretty exhausted. It doesn’t seem to matter how long he’s napped during the day for, what times he’s napped, if we’ve been in for the day, been to the park in the day etc. I’ve tried giving him an iPad to watch in his bed to hopefully fall asleep too, didn’t work, I’ve tried sitting next to bed with him having his fingers in my mouth, I’ve tried bringing him into my room. I’ve even tried leaving him in his room alone to cry for periods of time. Nothing works until HE decides he will finally give in. Then when he does, he will fall asleep and usually still wake up a while later, and still ends up in with me. I’m struggling massively as I like to try and make use of my evenings when he’s sleeping. It feels like I’m not getting much time from him and I’m also knackered but above all else we both ended up so worked up over this. Would appreciate any kind tips please guys. Thank you, one tired mumma