worried about my puppy

Hello everyone, Im New to this forum but I was worried about my 4 month puppy. Hes a American bulldog mix with possible wired haired terrier. His mom was hit and killed by a car and I saved the litter and raised them until I could get them adopted. All were adopted but one owner returned one. I now have him,and his name is Onyx. I also have a Chihuahua who is about 5 years old with no problems. That being said I m worried about the puppy because his stomach is swollen and bloated looking and feeling. Its been this way for about a week but it just keeps getting bigger. I done believe he has bloat. Hes not uncomfortable. And he has had worms in the past. He eats like a champ but hes had bad gas lately and his stools are loose but not watery. I found out recently that one of his siblings died from a stomach twist, but that was within hours of the incident. Any ideas from anyone?

Thank you in advance for your help.