I would suggest a button bath to clean his bottom, just to make everyone comfortable. Good job booking a vet appointment, in case anything is wrong. As far as his behavior goes, you said he’s only been with you a month, right, and you don’t know much about his life previous to you? My Yoshi had a hard time before I met her (neglect and mistreatment) and was very wary and distrustful of contact with myself and my husband- she would box, lunge, and Hite if we tried to go into her space or touch her. She’s calmed down a lot, but this behavior still flares up if she’s having a bad day. It might be something you need to work through with him. We did lots to reassure her, making sure she 100% never ran out of hay/water (some of her neglect was being deprived of these things ) and forcing her to interact with us in a small, neutral space, much like you would with bonding two rabbits. Also, when he bites, make sure you let him know it is not ok. Hope any of that helps