A.,
I remember being a first time mom and being concerned over EVERY thing....
Please BREATHE!! Please ENJOY your son! Don't rush him to grow up and meet the milestones...those milestones are not, repeat, NOT set in stone. Breathe.
My daughter will be 30 this August. She started laughing at 3 months - our dog would lick her face and she just thought that was hilarious!!
My son just turned 16. He started laughing around 4 months - maybe 5 - I would give him my GRUMPY face or read "where the W. things are" and I would GNASH MY TERRIBLE TEETH and ROAR my terrible roar!! He thought it was funny!
My youngest will be 14 in July. He laughed at his big brother falling over - that was about 4 months old - the ruckus scared/startled him and then he saw his brother's feet in the air - he laughed....
This happened in a blink of an eye - at least that's how it seemed - and those "terrible 2's" weren't so terrible - it was the Fearless 4's - those seemed to last for TWO YEARS...
Stop TRYING to get him to laugh. It WILL happen. The more you FORCE it? It won't be genuine. He doesn't know what you are TRYING to get him to do. Does he hear YOU laugh?? What about his daddy? Does he hear HIM laugh??
Please breathe. Let things happen when they happen. Milestones are a GUESSTIMATE - not a written in stone "thing"