Competitions symptoms and conditions

I am 14 years old and have been on singulair for 4 months at first i though it was helping but it was actully making it harder for me to do sports i have in the past 4 months had the flu, sinus infection, numbness in my arms and legs,throat and respitory infection and trouble sleeping at night. it doesn't help my swimming. I have competitions every 3 weeks and it is brining my mood down and most of the competitions I end up being sick. It is getting so bad that I cant go for more than 2 mineuts without coughing violently and I am constantly throwing up because it is so bad.