This is a bad situation. Is there any beeks near you that would let you have a frame of brood. I had the same issue last year and got a frame form my dad it made all the difference. I am one who prolly messes with the bees to much but I cant let one die if there is something I may be able to do. Last resort rob from one of the stronger hives if they are 3 1/2 weeks should be having new bees hatching by now. Just my 2 cents which is not worth much.