If this is the first time you have used the pump this season, then yep, it may take awhile to fill all the lines.
In my current rig I find that cycling a faucet open/closed for a few minutes in each position helps.
And a few times when I couldn't the pump to prime, I had to clean out the screen at the pump and then all was well.
And it's always a possibility that your pump has failed.
Scott and Liz - Southern NM
2012 Wildcat Sterling 32RL - w/level up (best option ever)
2007 Chevy 2500HD 4dr short bed Duramax w/allison
Reese Fifth Airborne air ride king pin coupler with Sidewinder