It's possible that he's going through a fear period, which some puppies do go through, or it's possible that he has nerve issues. Either way, take things slowly with him and don't ever force him to do anything he's afraid of. Keep your tone encouraging and upbeat, but don't try to comfort him when he's afraid. That only rewards the fear.
I have found that with my dogs, going up to the scary "thing" (be it a trash can, fire hydrant, horse statue in a yard, etc.) and acting like it's cool and no big deal, the puppy often follows. Do things to build his confidence as much as possible, and he should get over it.
Forrest - GSD 9/1/2016 - 5/14/2017 RIP
Brooklyn - Golden retriever 1/30/11