I started taking singulair 2 weeks ago and was surprised it worke...

I started taking singulair 2 weeks ago and was surprised it worked so quickly to relieve my allergy symptoms but then about 4 days into treatment i started feeling strange, i felt not like myself i could not explain it, well then one morning i noticed i was pale and then the muscle weakness began and then 2 days later i started getting bad muscle cramps and very bad muscle tightness in my back shoulder and neck.I stopped taking it 2 daays ago and right now i am suffering from terrible back muscle spasms.I think this medicine is a poison and the fda better take a better look at it.