On your style of bike you should just be able to tip-toe the ground while seating on the saddle. EG, when you come to a stop you shouldn't have to dismount but just put your toes down. This will setup you up properly when pedaling. The straight leg to heel adjustment is for road bikes and racing. BTW, when pedaling you want the ball of your foot centered on the pedal.

No breakfast and no water explains a lot. Much better to eat a 500 calorie breakfast (w/ maybe 10g of fiber minimum) before heading out. My guess is you'll enjoy your next ride a bit more. Also remember to take your time. There's no rush.