Hi Marie, I was quite uncomfortable myself before trigger. I was actually crying on the way to the RE the day before trigger b/c I felt so weird, and the u/s they did that day and the following were def on the painful side.
You are correct that the trigger is what fuels the hyperstimulation... supposedly you can't truly experience OHSS unless you do the trigger. Does your RE have you doing 10,000 units of hcg or 5000? My RE had me only do 5,000 b/c I was at a higher risk of developing OHSS. The good news is, I am 4 days post trigger and 2 days post E/R and I feel GREAT! Still bloated, but otherwise no problems (such as the shortness of breath and sudden weight gain). My RE has me tracking my weight daily, and I do that once in the morning and once at night... you might want to do that starting tomorrow since you do trigger tonite. Also, Holly is right... stay hydrated.... try to get some Smartwater since it has electrolytes... those electrolytes are good to fend off the OHSS.
Good luck, and try not to worry... think about the baby you are about to create!