I’m probably going to lose my job because of my sons behavior and I have no idea what the fuck else to do

I’m a single mom and have a 4yo and 1.5yo I nanny for the moment while attending school and have a 2.5 yo that I care for 4 days a week. My 4yo has absolutely unmanageable behavior, I feel like since he was 15 months it’s been just trying to avoid his horrible meltdowns (he used to bite and hit and thrash and throw his head back- now he hits, kicks, runs away, throws, pushes, slams, screams etc.) I have a call in for behavioral evaluation, but the initial eval they just said they couldn’t pinpoint a specific issue **they did say possibly adhd but would need further observation of him** . I’m getting to the point where I have tried everything, I have tried a whole brain approach, I’ve tried talking before/after, I’ve tried redirection, I’ve tried letting him think it out and have consequences and natural consequences when safe, I’ve tried time outs. taught him deep breaths and helped him identify emotions, I’ve tried a reward chart, i bought a body boundary book for him to learn about hitting, I’ve tried it freaking all. I’ve even tried spanking but it doesn’t do ANYTHING. It is JUST ME parenting him, he has no male or father figure or anyone else reinforcing what I’m enforcing. I’m EXAUSTED. And struggling staying grounded. I feel the urge to just hurt him so he feels the pain he’s inflicting on others, I definitely do NOT but I’m just saying that im at my very freaking end and don’t even know what to do and what’s what I feel at it’s worst. Instead I take a deep breath and bear hug around his flailing arms and sit him back in time out. I am feeling like I cannot connect with him and so fed up that I don’t have the energy to after I’ve dealt with his issues. I’m exhausted, fedup, and know for a fact it’s effecting the nanny family’s work because they work from home and he gets extremely loud when he’s having his meltdowns which seem to be at least 1 major time a day. I don’t need further judgement I do that enough on my own. Anyone have experience with behaviors like this? Managing them? Help a desperate mama out.