It happen to me also, the next department I went to asked my opinion on why I didn't get hired. I told them that I didn't get thru because I failed my poly. They gave me the poly, I passed and got hired.
As a general guideline you should begin with 20lb, and every 4 to 6 weeks go up 5 lbs until you get up to 40 lbs. But if at any time you feel that is too much pressure on your joints then go down on the weight.
Running on an empty stomach may cause you to run out of energy. I go with a couple of different options. Bagel with peanut butter, turkey on whole wheat bread, maybe a banana or an energy bar.