lasting side effects

I was given singulair by my doctor three months ago . after about eight days i started noticing side effects os head aches , dizziness , extreme tiredness , felt like i had the flu . stopped the singulair , but the symtoms continue , and seem to be getting worse . i was given the singulair to treat allergies . my doctor says it can't be caused by the singulair because i don't have a rash . ? i never had any of these symtoms before using singulair. i'm 63 years old and was in good health except for the allergies . one thing that makes me suspicious is none of my allergy symtoms have returned , even though i stopped taking singlair over twelve weeks ago . i now have a fever , blurred vision , dizziness , head aches , muscle aches , and drowsiness. haven't been able to get any answers from merck . if anyone out there has any info that would be helpfull , please send it along . thanks , and good luck if you're taking singulair