2 year old eats 1 meal a day... HEEELLLPPPP

I've tried everything. I cry every meal now because he'll only eat 1 meal a day: PBJ for lunch. He screams, cries, etc. He's been very picky for a year now. Lately he has dwindled down the few choices he would eat ... to absolutely nothing. Now he only eats a pbj for lunch. I read not to keep offering a variety of foods bc then he gets used to demanding something else to eat - it's either this or nothing. Well it has bitten me in the ass. He won't even take a gummy vitamin. He's refusing everything that I can't put his liquid vitamin in yogurt or oatmeal anymore.