He might just be reacting to a change in situations. I know he's only 3 mos old, but babies pick stuff up fast. (Plus I think it's all kid's missions to make their parents look as bad as possible in public

.) Also I think they become a bit more fussy in general at around that age--at least my 5 did. So be patient. He may up & decide it's ok someday. And just think, if you can get him to stop crying when you pick him up by the time he's 8 or 9 mos old--he'll be crying when you drop him off due to seperation anxiety. Mom's worries are never ending!!
Best of luck.