Hello and thank you for the question.
The 2 lumps you noticed were the swollen bulbo-cavernous muscles that allow the tie during mating.They are not testicles and are effected in no way by neutering.
Neutering will not prevent your dog from getting an erection it only prevents the production of sperm and lowers certain health and behavioral risks.
Once they have been neutered they no longer have the urge. The humping you are seeing is him trying to show his dominance over certain objects and people. Do not allow him to hump your leg, by doing this is he trying to tell you he is the boss or the alpha in the pack. You are the alpha and it is important that he know this.
Please do not worry all the signs you are seeing are very normal.Please let me know if I can be of additional assistance.
Candy
Veterinary Technician
Practicing Veterinary Technician for 23 years. Veterinary Practice Owner, Technician Trainer