Urgent advice needed

My son is currently living with us in a very small flat with his gf, baby and dog. The dog has become very aggressive with me. He bites me every time i go into the kitchen. I thought the problem was him being inside all the time in a very small space. Taking him out more hasnt helped. He is only aggressive to me. I have always been very kind to him, let him sleep in my bed when they are away, give him treats, never ever raised a hand to him or even my voice. Today he has hurt me badly, he bit my hand and i am now unable to move it. He is a big dog of mixed breeds and is not neutered which he should be. Any advice on this would help.