You don't give the exact location, but I had a small part of the scrotum get inside once, creating what appeared to be a bubble, with some sharp, pulling pain in the msame side testicle. If the 'bubble' was at the base, it may have been some scrotum skin. As far as just one whole side of the penis filling up, creating a bubble, I wonder if that is even possible, considering the nature and action of that part of the penis anatomy. Maybe others will join in if they have had this experience.
James C.