haha~ i guess the others explained the difference between 药片 and 药丸 clearly. The pet name is soooo cute and sweet^^ you could say ‘我的快乐小药丸’. It is an adorable pet name!

你好，伊丽莎白 the difference between "药丸" and "药片" is that their shapes are different.“丸”is something round, "片" means "a flat;thin piece;slice".“药丸”is“pill”in English,“药片”is“tablet”。 you mean the one who always makes you happy no matter what,am i right? XD "小快乐药丸" sounds weird for me,you can say "快乐药" or "开心药", but we often say "开心果" in Chinese.

很不幸，在中国没有这种说法，你这样说出来可能会让人莫名其妙`` 药丸与药片的区别：药丸是圆的或椭圆的，或至少有一边是圆的，而药片是扁的。

快乐小药丸 in Chinese ：仙丹。

well, you can say that like ：“我的快乐小药丸or 片”。because "little" is a size for the "pill", but the "happy" is your opinion. So the correct order of adj is opinion--size--noun. do you understand?