it does take longer to suck air than to suck water into the pump. Turn on a faucet and wait.
That you let it run dry means you might have gotten some debris in the pump. I have had this. Debris can cause the pump "flaps" to not be able to close fully and this means it is losing ability to pump / loss of pressure or loss of suction in this case.
If all else fails, take the head off the pump. The head is the dome shape black part that the pipes attach to. Take it all apart, it is quite simple. You will see 3 circle shapes in a rubber flap like thing. that is where the debris will be. Clean it all. Clean everything you can get to. reassemble. then prime.