I've Been Taking Mucinex For The Last Month Now, And

I've been taking Mucinex for the last month now, and I know you have to drink a complete glass of water with the pill(s). However, after I drink the entire glass of water, I end up getting strong gagging reflexes which leads to me throwing up all of the water. I also get this dry feeling behind my uvula, which makes it feel like a hair is in the back of my throat. Which doesn't make matters any better when trying to keep food down. Plus, now consistently coughing mu mucus all the time, and yet there's still no relief whatsoever. So what I'm saying is: no matter how much water I drink, it makes me feel worse than better. Do you know what is wrong with me? Thank you.