How can I prevent myself from sneezing right away?!

this is insane but after having untreatable allergies for 32 years! I've been through a lot - I don't know how to describe this but suck your tongue up to the roof of your mouth and hold it for a second - it alleviates pressure. Also you can press the sides of the top of your nose by your eyes but the tongue to roof of mouth method is most effective- I swear I am not making this up! it works!

I stop breathing for a bit (May sound sarcastic but no) and try to hold it in like that.

Think of a grapefruit.