Singulair and deja vu

My 2 year-old daughter is having similar behavior issues to those described here. Her doctor put her on Singulair in the spring, and we noticed a change in her behavior, so I took her off of it. Now, after having more asthma symptoms, a new pediatrician prescribed it to her again. When I told the doctor that it had turned our daughter into a monster when she took it before, the doctor said she didn't believe it was the medicine. Well, after one day of taking it this time, I told my husband that I was having deja vu, that our daughter was behaving exactly the same way. He said, "Well, she IS two"--implying that he didn't believe it was the medicine either. Well, yesterday, when he came home from work while she was in the middle of a horrible fit, he said, "Don't give her Singulair again." She is normally a sweet, well-rested, sociable little girl (yes, she is 2, but even if she throws a tantrum, she can usually be reasoned with or distracted. . . but not on Singulair). On Singulair she's a tantrum-throwing mess.