well aichin has also loooots of sweet love songs!! you should listen to Always Together, its sooo cute
and also Emi Hinouchi's Koi wa irurari! dunno it its a love song though, but its definatly sweet and will cheer you up!
also DBSK - box in the ship, and i dunno if this is a love song either but its soooooooo cute!!! you should really listen to it *ahhh goes off and plays it*
some others
kumi - always
sifow - ai-ai!
bae seulki - 사랑아 어떡한거니 (dunno if this is happy, but i find it sweet <3)
aaall of sunnyhill's songs!!
i can upload these songs if you want