Talk to Pediatrician on Child Mouth Ulcer

My 10 year old son had his lips corners cracked, i kept applying Vaseline, but it somehow spread to my younger son, he has it much worse, his lips are completely swollen, sides are cracked and bleeding, tongue us also sore and painful, he keeps crying constantly. I have taken him to two doctors who both prescribed multivitamins and Daktarin Oral Gel. But his condition is not getting any better but getting worse. Please help if any doctor can suggest something.