I have been on singulair for over 4 years with no side effects. ...

I have been on singulair for over 4 years with no side effects. Nothing but asthma that's totally under control. My 12 year old son has been on it on & off, when his allergys act up. He's been on 5mg a day regular for a couple of months straight. Last month I noticed my left eye was twitching often. Then about 2 weeks ago it went into a little spasm and was going on for about 80% of the day. It got so irritating I finally went to my interest, who gave me a muscle relaxer and said it would probably go away soon. A few nights ago my son showed me a twitch he had in his arm. It twitched all night. The only thing we have in common that I can think of is the Singulair. Wondering if it could be a side effect...?