Why don't I have any hits?
The "hit" is that slight throat contraction smokers crave; without it, you feel like you're just vaping flavored air. If you feel nothing, your nicotine level is too low or your device is set to "power-save" mode. Basically, your setup lacks punch, and your nerves are eventually going to snap.
Technically, the hit depends on nicotine concentration and the PG ratio. To boost it, increase your mod's wattage or choose a liquid with a higher PG content (e.g., 70/30). Also, ensure your airflow is properly adjusted: a tighter draw usually concentrates the throat sensation better.