Stuffy and congested the second I eat

As soon as i eat, or take a gulp of water, anything, my nose gets completely stuffy and blocked, and I can feel my sinus's being swollen. WHY?

I also have post-nasal drip which is also hell. Related?

can it really be an intolerance to something i'm eating when I get it from a sip of water? really?

Thanks all.

[Caryopteris]

It makes me think you have a swallowing dysfunction.  You would need a swallowing study for that.  Stopping dairy MIGHT help, no matter what the cause.  

[margypops]

allergies. probably environmental ..