Give it time... your baby should show more happy behavior in months 3 and 4. Try not to worry about all the other happy babies you see. I know it's hard, though. My first didn't roll over (either direction) until she was over 9 months old! I couldn't believe all the tiny babies I saw rolling over and was so worried! (She turned out just fine).
In the meantime, try singing to baby and try to forget about it ... it will come.