Singulair and charley horse

My seven year old son has been on Singulair for a year and half. He would get angry but he's a kid...and I didn't think anything of it. Then the headaches and bad dreams....and then he's always talking about death. One day, I wasn't home when he arrived from school and he met me at the door crying....he thought I was dead. But the muscles cramps really got me. He's to young for cramps and waking up with a charley horse. I took him to the clinic and to the ER twice.. and still the doctors don't know why he's getting muscle cramps. So I said...let me go online to find some answers. Well... you know I'm going to his doctor and I threw his bottle of Singulair away. I'm going to start a journal and chart his progress and I'll get back to y'all.