Son won't sleep and I'm going to lose my mind

I work full time and we pay my sister in law to babysit. She said he hasn't napped on a week which I believe because he won't nap on weekends! Not only that, but I have been running on 2.5-3 hours of sleep a night for the last 2 weeks. I'm at my breaking point. I try to wear him out, give him lavender baths, snuggle and watch a movie. I even took him to the doctor on Black Friday and that said he's fine... I can't keep going like this. I feel half alive, severely run down, exhausted, and I've cried multiple times tonight.