Why do I feel this way when I jog now?

Definitely dehydration. I had an intense ab cramp when the temperature went up to 95� after being a cool 70� for weeks. My body wasn't used to it, and I sweat a ton, dehydratin myself, AND losing electrolytes. If it's been getting warmer where you live, I would drink more water throughout the day and 30 mins before running. After your runs, I would drink some gatorade until your body adjusts itself and can deal with electrolyte imbalances in the heat.